U.S. patent application number 13/417998 was filed with the patent office on 2012-09-20 for laser diode element assembly and method of driving the same.
This patent application is currently assigned to TOHOKU UNIVERSITY. Invention is credited to Rintaro Koda, Masaru Kuramoto, Tomoyuki Oki, Hideki Watanabe, Hiroyuki Yokoyama.
Application Number | 20120236886 13/417998 |
Document ID | / |
Family ID | 46815623 |
Filed Date | 2012-09-20 |
United States Patent
Application |
20120236886 |
Kind Code |
A1 |
Oki; Tomoyuki ; et
al. |
September 20, 2012 |
LASER DIODE ELEMENT ASSEMBLY AND METHOD OF DRIVING THE SAME
Abstract
A laser diode element assembly includes: a laser diode element;
and a light reflector, in which the laser diode element includes
(a) a laminate structure body configured by laminating, in order, a
first compound semiconductor layer of a first conductivity type
made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type, (b) a second
electrode formed on the second compound semiconductor layer, and
(c) a first electrode electrically connected to the first compound
semiconductor layer, the laminate structure body includes a ridge
stripe structure, and a minimum width W.sub.min and a maximum width
W.sub.max of the ridge stripe structure satisfy
1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3.
Inventors: |
Oki; Tomoyuki; (Kanagawa,
JP) ; Kuramoto; Masaru; (Kanagawa, JP) ; Koda;
Rintaro; (Tokyo, JP) ; Watanabe; Hideki;
(Kanagawa, JP) ; Yokoyama; Hiroyuki; (Miyagi,
JP) |
Assignee: |
TOHOKU UNIVERSITY
Miyagi
JP
SONY CORPORATION
Tokyo
JP
|
Family ID: |
46815623 |
Appl. No.: |
13/417998 |
Filed: |
March 12, 2012 |
Current U.S.
Class: |
372/38.02 ;
372/44.01 |
Current CPC
Class: |
H01S 5/0625 20130101;
H01S 5/3063 20130101; H01S 5/0602 20130101; B82Y 20/00 20130101;
H01S 5/1085 20130101; H01S 2301/166 20130101; H01S 5/04252
20190801; H01S 5/34333 20130101; H01S 5/1064 20130101 |
Class at
Publication: |
372/38.02 ;
372/44.01 |
International
Class: |
H01S 5/062 20060101
H01S005/062; H01S 5/028 20060101 H01S005/028 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2011 |
JP |
2011-058899 |
Claims
1. A laser diode element assembly comprising: a laser diode
element; and a light reflector, wherein the laser diode element
includes (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type, (b) a second
electrode formed on the second compound semiconductor layer, and
(c) a first electrode electrically connected to the first compound
semiconductor layer, the laminate structure body includes a ridge
stripe structure, laser light is emitted from a first end surface
of the ridge stripe structure, and a part of the laser light is
reflected by the light reflector to be returned to the laser diode
element, and a remaining part of the laser light exits to outside
through the light reflector, the laser light is reflected by a
second end surface of the ridge stripe structure, and a minimum
width W.sub.min and a maximum width W.sub.max of the ridge stripe
structure satisfy 1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3.
2. A laser diode element assembly comprising: a laser diode
element; and a light reflector, wherein the laser diode element
includes (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type, (b) a second
electrode formed on the second compound semiconductor layer, and
(c) a first electrode electrically connected to the first compound
semiconductor layer, the laminate structure body includes a ridge
stripe structure, laser light is emitted from a first end surface
of the ridge stripe structure, and the laser light is reflected by
the light reflector to be returned to the laser diode element, a
part of the laser light exits to outside from a second end surface
of the ridge stripe structure, and a minimum width W.sub.min and a
maximum width W.sub.max of the ridge stripe structure satisfy
1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3.
3. A laser diode element assembly comprising: a laser diode
element; and an external resonator, wherein the laser diode element
includes (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type, (b) a second
electrode formed on the second compound semiconductor layer, and
(c) a first electrode electrically connected to the first compound
semiconductor layer, the laminate structure body includes a ridge
stripe structure, laser light is emitted from a first end surface
of the ridge stripe structure, and the laser light is reflected by
the external resonator to be returned to the laser diode element,
laser light emitted from the first end surface or a second end
surface of the ridge stripe structure exits to outside, and a
minimum width W.sub.min and a maximum width W.sub.max of the ridge
stripe structure satisfy 1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3.
4. The laser diode element assembly according to claim 1, wherein
the light reflector is configured of a mirror, a chirped mirror, a
volume Bragg grating, or a fiber Bragg grating.
5. The laser diode element assembly according to claim 1, wherein
the laser light exiting to outside is single-mode light.
6. The laser diode element assembly according to claim 1, wherein
1.times.10.sup.-6 m.ltoreq.W.sub.min.ltoreq.3.times.10.sup.-6 m is
satisfied.
7. The laser diode element assembly according to claim 1, wherein
the third compound semiconductor layer further includes a saturable
absorption region, the second electrode is configured of a first
section and a second section, the first section configured to
create a forward bias state by passing a current to the first
electrode through the light emission region, the second section
configured to apply an electric field to the saturable absorption
region, and the first section and the second section of the second
electrode are separated by a separation groove.
8. The laser diode element assembly according to claim 7, wherein
the saturable absorption region is disposed in a portion of the
laminate structure body, the portion located closer to an end
surface opposite to an end surface where laser light exits to
outside.
9. The laser diode element assembly according to claim 7, wherein
the laser light exiting to outside is pulsed oscillation laser
light.
10. The laser diode element assembly according to claim 9, wherein
the saturable absorption region is disposed in a portion of the
laminate structure body, the portion located closer to an end
surface opposite to an end surface where laser light exits to
outside.
11. The laser diode element assembly according to claim 1, wherein
the laser light exiting to outside is continuous-wave oscillation
laser light.
12. The laser diode element assembly according to claim 1, wherein
light intensity E.sub.out of laser light emitted from the laser
diode element assembly satisfies E.sub.out/E.sub.01.5, where light
intensity of laser light exiting to outside assuming that
W.sub.min=W.sub.max is established is E.sub.0.
13. A method of driving a laser diode element assembly, the laser
diode element assembly including a laser diode element and a light
reflector, the laser diode element including (a) a laminate
structure body configured by laminating, in order, a first compound
semiconductor layer of a first conductivity type made of a
GaN-based compound semiconductor, a third compound semiconductor
layer made of a GaN-based compound semiconductor and including a
light emission region, and a second compound semiconductor layer of
a second conductivity type made of a GaN-based compound
semiconductor, the second conductivity type being different from
the first conductivity type, (b) a second electrode formed on the
second compound semiconductor layer, and (c) a first electrode
electrically connected to the first compound semiconductor layer,
the third compound semiconductor layer further including a
saturable absorption region, the second electrode being configured
of a first section and a second section, the first section
configured to create a forward bias state by passing a current to
the first electrode through the light emission region, the second
section configured to apply an electric field to the saturable
absorption region, the first section and the second section of the
second electrode being separated by a separation groove, the
laminate structure body including a ridge stripe structure, laser
light being emitted from a first end surface of the ridge stripe
structure, and a part of the laser light being reflected by the
light reflector to be returned to the laser diode element, and a
remaining part of the laser light exiting to outside through the
light reflector, the laser light being reflected by a second end
surface of the ridge stripe structure, a minimum width W.sub.min
and a maximum width W.sub.max of the ridge stripe structure
satisfying 1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3, the method comprising:
while passing a current to the first electrode through the first
section of the second electrode and the light emission region,
passing a current to the second section of the second electrode
through the first electrode and the saturable absorption region,
thereby allowing pulsed oscillation to be performed; and while
passing a current to the first electrode through the first section
of the second electrode and the light emission region, passing a
current to the first electrode through the second section of the
second electrode and the light emission region, or not passing a
current to the first electrode through the second section of the
second electrode and the light emission region, thereby allowing
continuous-wave oscillation to be performed.
14. A method of driving a laser diode element assembly, the laser
diode element assembly including a laser diode element and a light
reflector, the laser diode element including (a) a laminate
structure body configured by laminating, in order, a first compound
semiconductor layer of a first conductivity type made of a
GaN-based compound semiconductor, a third compound semiconductor
layer made of a GaN-based compound semiconductor and including a
light emission region, and a second compound semiconductor layer of
a second conductivity type made of a GaN-based compound
semiconductor, the second conductivity type being different from
the first conductivity type, (b) a second electrode formed on the
second compound semiconductor layer, and (c) a first electrode
electrically connected to the first compound semiconductor layer,
the third compound semiconductor layer further including a
saturable absorption region, the second electrode being configured
of a first section and a second section, the first section
configured to create a forward bias state by passing a current to
the first electrode through the light emission region, the second
section configured to apply an electric field to the saturable
absorption region, the first section and the second section of the
second electrode being separated by a separation groove, the
laminate structure body including a ridge stripe structure, laser
light being emitted from a first end surface of the ridge stripe
structure, and the laser light being reflected by the light
reflector to be returned to the laser diode element, a part of the
laser light exiting to outside from a second end surface of the
ridge stripe structure, a minimum width and a maximum width
W.sub.max of the ridge stripe structure satisfying
1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3, the method comprising:
while passing a current to the first electrode through the first
section of the second electrode and the light emission region,
passing a current to the second section of the second electrode
through the first electrode and the saturable absorption region,
thereby allowing pulsed oscillation to be performed; and while
passing a current to the first electrode through the first section
of the second electrode and the light emission region, passing a
current to the first electrode through the second section of the
second electrode and the light emission region, or not passing a
current to the first electrode through the second section of the
second electrode and the light emission region, thereby allowing
continuous-wave oscillation to be performed.
15. A method of driving a laser diode element assembly, the laser
diode element assembly including a laser diode element and an
external resonator, the laser diode element including (a) a
laminate structure body configured by laminating, in order, a first
compound semiconductor layer of a first conductivity type made of a
GaN-based compound semiconductor, a third compound semiconductor
layer made of a GaN-based compound semiconductor and including a
light emission region, and a second compound semiconductor layer of
a second conductivity type made of a GaN-based compound
semiconductor, the second conductivity type being different from
the first conductivity type, (b) a second electrode formed on the
second compound semiconductor layer, and (c) a first electrode
electrically connected to the first compound semiconductor layer,
the third compound semiconductor layer further including a
saturable absorption region, the second electrode being configured
of a first section and a second section, the first section
configured to create a forward bias state by passing a current to
the first electrode through the light emission region, the second
section configured to apply an electric field to the saturable
absorption region, the first section and the second section of the
second electrode being separated by a separation groove, the
laminate structure body including a ridge stripe structure, laser
light being emitted from a first end surface of the ridge stripe
structure, and the laser light being reflected by the external
resonator to be returned to the laser diode element, laser light
emitted from the first end surface or a second end surface of the
ridge stripe structure exiting to outside, a minimum width
W.sub.min and a maximum width W.sub.max of the ridge stripe
structure satisfying 1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3, the method comprising:
while passing a current to the first electrode through the first
section of the second electrode and the light emission region,
passing a current to the second section of the second electrode
through the first electrode and the saturable absorption region,
thereby allowing pulsed oscillation to be performed; and while
passing a current to the first electrode through the first section
of the second electrode and the light emission region, passing a
current to the first electrode through the second section of the
second electrode and the light emission region, or not passing a
current to the first electrode through the second section of the
second electrode and the light emission region, thereby allowing
continuous-wave oscillation to be performed.
16. The method of driving a laser diode element assembly according
to claim 13, wherein the saturable absorption region is disposed in
a portion of the laminate structure body, the portion located
closer to an end surface opposite to an end surface where laser
light exits to outside.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present application claims priority to Japanese Priority
Patent Application JP 2011-058899 filed in the Japan Patent Office
on Mar. 17, 2011, the entire content of which is hereby
incorporated by reference.
BACKGROUND
[0002] The present application relates to a laser diode element
assembly and a method of driving the same.
[0003] Recently, for researches in a leading-edge science region
using laser light of pulse duration in the attosecond range or the
femtosecond range, ultrashort-pulse/ultrahigh-power lasers have
been frequently used. Moreover, a high-power/ultrashort-pulse laser
diode element with a light emission wavelength of 405 nm made of a
GaN-based compound semiconductor is expected to serve as a light
source of a volumetric optical disk system which is expected as a
next-generation optical disk system following a Blu-ray optical
disk system, or a light source necessary in the medical field, the
bio-imaging field, or the like.
[0004] As the ultrashort-pulse/ultrahigh-power laser, for example,
a titanium/sapphire laser is known; however, the titanium/sapphire
laser is an expensive and large solid laser light source, which is
a main impediment to the spread of the technology. If the
ultrashort-pulse/ultrahigh-power laser is realized through the use
of a laser diode or a laser diode element, it is considered that a
large reduction in size, price, and power consumption of the
ultrashort-pulse/ultrahigh-power laser, and high stability of the
ultrashort-pulse/ultrahigh-power laser will be achieved, thereby
leading to a breakthrough in promoting widespread use of the
ultrashort-pulse/ultrahigh-power laser in these fields.
[0005] On the other hand, an attempt to shorten pulses from a laser
diode element has been actively studied since 1960s in the
communications field. As a method of generating short pulses in a
laser diode element, a gain switching method, a loss switching
method (a Q switching method), and a mode-locking method are known,
and in these methods, the laser diode element is combined with a
semiconductor amplifier, a nonlinear optical element, an optical
fiber, or the like to aim at achieving higher power. Mode-locking
is further classified into active mode-locking and passive
mode-locking. To generate optical pulses based on the active
mode-locking, an external resonator structure is configured of a
laser diode element with use of a mirror or a lens, and
radio-frequency (RF) modulation is applied to the laser diode
element. On the other hand, in the passive mode-locking, when a
laser diode element with a multielectrode structure is used,
optical pulses are allowed to be generated by a simple DC
drive.
[0006] In laser light sources, achieving higher power is a major
issue. In addition, for the convenience of using the laser diode
element as a light source, it is frequently desired that laser
light emitted from the laser diode element be single-mode light.
These issues are major issues in not only pulsed oscillation of
laser light but also continuous-wave oscillation. As a method of
amplifying light from a laser light source, a semiconductor optical
amplifier (SOA) is considered. Herein, the optical amplifier is an
amplifier which directly amplifies an optical signal in the form of
light without converting the optical signal into an electrical
signal, and the optical amplifier has a laser structure without a
resonator, and amplifies incident light by an optical gain thereof.
However, to reduce manufacturing cost, a light source with a simple
configuration without optical components such as an optical
amplifier is strongly desired.
SUMMARY
[0007] To achieve stabilization in a drive of a laser diode element
based on a mode-locking method or a size reduction in the laser
diode element, laser diode element assemblies with an external
resonator are known from, for example, Japanese Unexamined Patent
Application Publication Nos. 2002-164614 and 2006-041400. However,
in these patent documents, a technique of achieving higher power is
not mentioned.
[0008] Therefore, it is desirable to provide a laser diode element
assembly capable of achieving higher power and emitting laser
light, and a method of driving the laser diode element
assembly.
[0009] According to a first or second embodiment of the
application, there is provided a laser diode element assembly
including: a laser diode element; and a light reflector,
[0010] in which the laser diode element includes
[0011] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0012] (b) a second electrode formed on the second compound
semiconductor layer, and
[0013] (c) a first electrode electrically connected to the first
compound semiconductor layer, and
[0014] the laminate structure body includes a ridge stripe
structure.
[0015] In the laser diode element assembly according to the first
embodiment of the application, laser light is emitted from a first
end surface of the ridge stripe structure, and a part of the laser
light is reflected by the light reflector to be returned to the
laser diode element, and a remaining part of the laser light exits
to outside through the light reflector, the laser light is
reflected by a second end surface of the ridge stripe structure,
and a minimum width W.sub.min and a maximum width W.sub.max of the
ridge stripe structure satisfy 1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3. It is to be noted that
the width on the first end surface of the ridge stripe structure
and the width on the second end surface of the ridge stripe
structure are preferably, but not exclusively, the maximum width
W.sub.max, and the minimum width W.sub.min, respectively. The same
applies to a method of driving a laser diode element assembly
according to a first embodiment of the application which will be
described later.
[0016] In the laser diode element assembly according to the second
embodiment of the application, laser light is emitted from a first
end surface of the ridge stripe structure, and the laser light is
reflected by the light reflector to be returned to the laser diode
element, a part of the laser light exits to outside from the second
end surface of the ridge stripe structure, and a minimum width
W.sub.min and a maximum width W.sub.max of the ridge stripe
structure satisfy 1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3. It is to be noted that
the width on the first end surface of the ridge stripe structure
and the width on the second end surface of the ridge stripe
structure are preferably, but not exclusively, the maximum width
W.sub.max, and the minimum width W.sub.min, respectively. The same
applies to a method of driving a laser diode element assembly
according to a second embodiment of the application which will be
described later.
[0017] According to a third embodiment of the application, there is
provided a laser diode element assembly including: a laser diode
element; and an external resonator,
[0018] in which the laser diode element includes
[0019] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0020] (b) a second electrode formed on the second compound
semiconductor layer, and
[0021] (c) a first electrode electrically connected to the first
compound semiconductor layer,
[0022] the laminate structure body includes a ridge stripe
structure,
[0023] laser light is emitted from a first end surface of the ridge
stripe structure, and the laser light is reflected by the external
resonator to be returned to the laser diode element,
[0024] laser light emitted from the first end surface or a second
end surface of the ridge stripe structure exits to outside, and
[0025] a minimum width W.sub.min and a maximum width W.sub.max of
the ridge stripe structure satisfy 1<W.sub.max/W.sub.min<3.3
or 6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3.
[0026] It is to be noted that the width on the first end surface of
the ridge stripe structure and the width on the second end surface
of the ridge stripe structure are preferably, but not exclusively,
the maximum width W.sub.max, and the minimum width W.sub.min,
respectively. The same applies to a method of driving a laser diode
element assembly according to a third embodiment of the application
which will be described later.
[0027] According to the first or second embodiment of the
application, there is provided a method of driving a laser diode
element assembly, the laser diode element assembly including a
laser diode element and a light reflector, the laser diode element
including
[0028] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0029] (b) a second electrode formed on the second compound
semiconductor layer, and
[0030] (c) a first electrode electrically connected to the first
compound semiconductor layer,
[0031] the third compound semiconductor layer further including a
saturable absorption region,
[0032] the second electrode being configured of a first section and
a second section, the first section configured to create a forward
bias state by passing a current to the first electrode through the
light emission region, the second section configured to apply an
electric field to the saturable absorption region,
[0033] the first section and the second section of the second
electrode being separated by a separation groove, and
[0034] the laminate structure body including a ridge stripe
structure,
[0035] in the method of driving a laser diode element assembly
according to the first embodiment of the application, in the laser
diode element assembly, laser light is emitted from a first end
surface of the ridge stripe structure, and a part of the laser
light is reflected by the light reflector to be returned to the
laser diode element, and a remaining part of the laser light exits
to outside through the light reflector, and
[0036] the laser light is reflected by a second end surface of the
ridge stripe structure, and
[0037] a minimum width W.sub.min and a maximum width W.sub.max of
the ridge stripe structure satisfy 1<W.sub.max/W.sub.min<3.3
or 6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3, and
[0038] in the method of driving a laser diode element assembly
according to the second embodiment of the application, in the laser
diode element assembly, laser light is emitted from a first end
surface of the ridge stripe structure, and the laser light is
reflected by the light reflector to be returned to the laser diode
element,
[0039] a part of the laser light exits to outside from a second end
surface of the ridge stripe structure, and
[0040] a minimum width W.sub.min and a maximum width W.sub.max of
the ridge stripe structure satisfy 1<W.sub.max/W.sub.min<3.3
or 6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3.
[0041] The method of driving a laser diode element assembly
according to the first or second embodiment of the application
includes:
[0042] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the second section of the second
electrode through the first electrode and the saturable absorption
region, thereby allowing pulsed oscillation to be performed;
and
[0043] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the first electrode through the second
section of the second electrode and the light emission region, or
not passing a current to the first electrode through the second
section of the second electrode and the light emission region,
thereby allowing continuous-wave oscillation to be performed.
[0044] It is to be noted that "passing a current" is equivalent to
applying a voltage. The same applies to the following description.
Moreover, in the case where, while a current is passed to the first
electrode through the first section of the second electrode and the
light emission region, a current is passed to the first electrode
through the second section of the second electrode and the light
emission region, for example, the first section and the second
section of the second electrode may be short-circuited. The same
applies to the following embodiment. It is to be noted that pulsed
oscillation is preferably single-mode pulsed oscillation, and
continuous-wave oscillation is preferably single-mode
continuous-wave oscillation. The same applies to the following
embodiment.
[0045] According to a third embodiment of the application, there is
provided a method of driving a laser diode element assembly, the
laser diode element assembly including a laser diode element and an
external resonator, the laser diode element including
[0046] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0047] (b) a second electrode formed on the second compound
semiconductor layer, and
[0048] (c) a first electrode electrically connected to the first
compound semiconductor layer,
[0049] the third compound semiconductor layer further including a
saturable absorption region,
[0050] the second electrode being configured of a first section and
a second section, the first section configured to create a forward
bias state by passing a current to the first electrode through the
light emission region, the second section configured to apply an
electric field to the saturable absorption region,
[0051] the first section and the second section of the second
electrode being separated by a separation groove,
[0052] the laminate structure body including a ridge stripe
structure,
[0053] laser light being emitted from a first end surface of the
ridge stripe structure, and the laser light being reflected by the
external resonator to be returned to the laser diode element,
[0054] laser light emitted from the first end surface or a second
end surface of the ridge stripe structure exiting to outside, a
minimum width W.sub.min and a maximum width W.sub.max of the ridge
stripe structure satisfying 1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3,
[0055] the method including:
[0056] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the second section of the second
electrode through the first electrode and the saturable absorption
region, thereby allowing pulsed oscillation to be performed;
and
[0057] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the first electrode through the second
section of the second electrode and the light emission region, or
not passing a current to the first electrode through the second
section of the second electrode and the light emission region,
thereby allowing continuous-wave oscillation to be performed.
[0058] In the laser diode element assemblies and the methods of
driving a laser diode element assembly according to the first to
third embodiments of the application, the ridge stripe structure
having an external resonator structure and having a so-called flare
structure with a specified relationship between the minimum width
W.sub.min and the maximum width W.sub.max is included; therefore,
higher power is allowed to be achieved.
[0059] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the application
as claimed.
[0060] Additional features and advantages are described herein, and
will be apparent from the following Detailed Description and the
figures.
BRIEF DESCRIPTION OF THE FIGURES
[0061] The accompanying drawings are included to provide a further
understanding of the disclosure, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments and, together with the specification, serve to explain
the principles of the technology.
[0062] FIGS. 1A and 1B are conceptual diagrams of a laser diode
element assembly of Example 1 and FIG. 1C is a schematic plan view
of a laser diode element in Example 1 or Example 2.
[0063] FIGS. 2A and 2B are schematic plan views of modifications of
the laser diode element in Example 1 or Example 2.
[0064] FIG. 3 is a schematic end view of the laser diode element in
Example 1 or Example 2 taken along a direction where a resonator
extends (a schematic end view taken along a XZ plane).
[0065] FIG. 4 is a schematic sectional view of the laser diode
element in Example 1 or Example 2 taken along a direction
perpendicular to the direction where the resonator extends (a
schematic sectional view taken along a YZ plane).
[0066] FIGS. 5A and 5B are conceptual diagrams of a laser diode
element assembly of Example 2.
[0067] FIGS. 6A and 6B are diagrams illustrating near-field images
in pulsed oscillation and a near-field image in continuous-wave
oscillation in the case of (W.sub.min, W.sub.max)=(1.5 .mu.m, 2.5
.mu.m) (Example 1A), respectively.
[0068] FIGS. 7A to 7C are diagrams illustrating a near-field image
in pulsed oscillation and a near-field image in continuous-wave
oscillation in the case of (W.sub.min, W.sub.max)=(1.5 .mu.m, 5.0
.mu.m) (Reference Example 1B), and a near-field image in
Comparative Example 1B, respectively.
[0069] FIGS. 8A to 8C are diagrams illustrating a near-field image
in pulsed oscillation and a near-field image in continuous-wave
oscillation in the case of (W.sub.min, W.sub.max)=(1.5 .mu.m, 10.0
.mu.m) (Example 1C), and a near-field image in Comparative Example
1C, respectively.
[0070] FIGS. 9A to 9C are diagrams illustrating a near-field image
in pulsed oscillation and a near-field image in continuous-wave
oscillation in the case of (W.sub.min, W.sub.max)=(1.5 .mu.m, 15.0
.mu.m) (Example 1D), and a near-field image in Comparative Example
1D, respectively.
[0071] FIGS. 10A to 10C are diagrams illustrating a near-field
image in pulsed oscillation and a near-field image in
continuous-wave oscillation in the case of (W.sub.min,
W.sub.max)=(1.5 .mu.m, 20.0 .mu.m) (Example 1E), and a near-field
image in Comparative Example 1E, respectively.
[0072] FIGS. 11A to 11C are diagrams illustrating a near-field
image in pulsed oscillation and a near-field image in
continuous-wave oscillation in the case of (W.sub.min,
W.sub.max)=(2.5 .mu.m, 15.0 .mu.m) (Example 1F), and a near-field
image in Comparative Example 1F, respectively.
[0073] FIG. 12 is a graph illustrating a relationship in the laser
diode element assembly of Example 1 between a width of a ridge
stripe structure and pulse energy of laser light emitted from the
laser diode element assembly in pulsed oscillation.
[0074] FIG. 13 is a schematic end view of a modification of the
laser diode element in Example 1 or Example 2 taken along a
direction where a resonator extends (a schematic end view taken
along an XZ plane).
[0075] FIG. 14 is a schematic top view of a ridge stripe structure
of a modification of the laser diode element in Example 1 or
Example 2.
[0076] FIGS. 15A and 15B are schematic partial sectional views of a
substrate and the like for describing a method of manufacturing the
laser diode element in Example 1.
[0077] FIGS. 16A and 16B are schematic partial sectional views of
the substrate and the like for describing the method of
manufacturing the laser diode element in Example 1 following FIG.
15B.
[0078] FIG. 17 is a schematic partial end view of the substrate and
the like for describing the method of manufacturing the laser diode
element in Example 1 following FIG. 16B.
[0079] FIGS. 18A and 18B are schematic plan views of modifications
of the laser diode elements in Example 1 or Example 2.
DETAILED DESCRIPTION
[0080] The present application will be described referring to
examples and the accompanying drawings; however, the application is
not limited thereto, and various values and materials in the
examples are given by way of illustration. It is to be noted that
description will be given in the following order.
1. Laser diode element assemblies and methods of driving the same
according to first to third embodiments of the present application,
and general description 2. Example 1 (Laser diode element
assemblies and methods of driving the same according to the first
and third embodiments of the application) 3. Example 2 (Laser diode
element assemblies and methods of driving the same according to the
second and third embodiments of the application), and others
Laser Diode Element Assemblies and Methods of Driving the Same
According to First to Third Embodiment of the Present Application,
and General Description
[0081] In laser diode element assemblies according to first to
third embodiments of the application, or methods of driving a laser
diode element assembly according to first to third embodiments of
the application, a light reflector or an external resonator may be
configured of a mirror (a half mirror in the laser diode element
assemblies according to the first and third embodiments of the
application or the methods of driving a laser diode element
assembly according to the first and third embodiments of the
application, a total reflection mirror in the laser diode element
assembly or the method of driving the same according to the second
embodiment of the application), a chirped mirror, a volume Bragg
grating (VBG), or a fiber Bragg grating (FBG).
[0082] In the laser diode element assemblies according to the first
to third embodiments of the application including the
above-described preferred configuration, or the methods of driving
a laser diode element assembly according to the first to third
embodiments of the application, laser light exiting to outside is
preferably single-mode light. Herein, "single-mode"
(single-transverse-mode) means that one or more light intensity
peaks are observed in a light intensity distribution of a
near-field image in a transverse mode, and the light intensity of
one of the light intensity peaks constitutes 80% or more,
preferably 90% or more of total light intensity.
[0083] In the laser diode element assemblies according to the first
to third embodiments of the application including the
above-described preferred configurations, or the methods of driving
a laser diode element assembly according to the first to third
embodiments of the application, as described above, a ridge stripe
structure has a so-called flare structure, and a minimum width
W.sub.min, of the ridge stripe structure preferably satisfies
1.times.10.sup.-6 m. In the case where the minimum width W.sub.min,
is smaller than 1.times.10.sup.-6 m, a laser diode element assembly
having a desired light intensity may not be obtained, and in the
case where the minimum width W.sub.min exceeds 3.times.10.sup.-6 m,
laser light emitted from the laser diode element assembly may not
become single-mode light. When the minimum width W.sub.min, of the
ridge stripe structure is within the above-described range,
single-transverse-mode laser light is obtainable.
[0084] Moreover, in the laser diode element assemblies according to
the first to third embodiments of the application including the
above-described various preferred configurations, a third compound
semiconductor layer may further include a saturable absorption
region, and a second electrode may be configured of a first section
and a second section, the first section configured to create a
forward bias state by passing a current to a first electrode
through a light emission region, the second section configured to
apply an electric field to the saturable absorption region, and the
first section and the second section of the second electrode may be
separated by a separation groove. It is to be noted that, for the
sake of convenience, a laser diode element with such a
configuration and such a structure, or a laser diode element in the
methods of driving a laser diode element assembly according to the
first to third embodiments of the application may be referred to as
"multielectrode type laser diode element". In the multielectrode
type laser diode element in the laser diode element assemblies
according to the first to third embodiments of the application,
laser light exiting to outside may be pulsed oscillation laser
light. It is to be noted that, in the multielectrode type laser
diode element including such a mode, or in the methods of driving a
laser diode element assembly according to the first to third
embodiments of the application including the above-described
preferred configurations, the saturable absorption region is
preferably disposed in a portion of a laminate structure body, the
portion disposed closer to an end surface opposite to an end
surface facing the light reflector or the external resonator (an
end surface where laser light exits to outside), or the saturable
absorption region is preferably disposed closer to an end surface
opposite to an end surface where laser light exit to outside in the
laminate structure body.
[0085] Alternatively, in the laser diode element assemblies
according to the first to third embodiments of the application
including the above-described preferred configurations, modes and
the multielectrode type laser diode element, laser light exiting to
outside may be continuous-wave oscillation laser light. In the case
where laser light exiting to outside from the multielectrode type
laser diode element is continuous-wave oscillation laser light, for
example, the first section and the second section of the second
electrode may be short-circuited, or alternatively, a current may
not be passed to the second section of the second electrode.
[0086] In the laser diode element assemblies or the methods of
driving the same according to the first to third embodiments of the
application including the above-described preferred configurations
and modes, it is desirable that light intensity E.sub.out of laser
light emitted from the laser diode element assembly satisfy
E.sub.out/E.sub.0.gtoreq.1.5, where light intensity of laser light
exiting to outside assuming that W.sub.min=W.sub.max is established
is E.sub.0.
[0087] In the multielectrode type laser diode element including the
above-described preferred various configurations and modes, it is
desirable that electrical resistance between the first section and
the second section of the second electrode be 1.times.10 times or
more, preferably 1.times.10.sup.2 times or more, more preferably
1.times.10.sup.3 times or more as high as electrical resistance
between the second electrode and the first electrode.
Alternatively, it is desirable that the electrical resistance
between the first section and the second section of the second
electrode be 1.times.10.sup.2.OMEGA. or more, preferably
1.times.10.sup.3.OMEGA. or more, more preferably
1.times.10.sup.4.OMEGA. or more.
[0088] In such a multielectrode type laser diode element, the
electrical resistance between the first section and the second
section of the second electrode is 1.times.10 times or more as high
as the electrical resistance between the second electrode and the
first electrode, or 1.times.10.sup.2.OMEGA. or more. Therefore, a
leakage current flowing from the first section of the second
electrode to the second section is allowed to be reliably
suppressed. In other words, a reverse bias voltage applied to the
saturable absorption region (carrier non-injection region) is
allowed to be increased for pulsed oscillation; therefore, a
mode-locking operation in a single mode having laser light of short
pulse duration is achievable. Then, such high electrical resistance
between the first section and the second section of the second
electrode is achievable only by separating the second electrode
into the first section and the second section by the separation
groove.
[0089] Moreover, in the multielectrode type laser diode element
including the above preferred configurations and modes, the third
compound semiconductor layer may have, but not limited to, a
quantum well structure including a well layer and a barrier layer,
and the thickness of the well layer is within a range of 1 nm to 10
nm both inclusive, preferably within a range of 1 nm to 8 nm both
inclusive, and the doping concentration of an impurity in the
barrier layer is within a range of 2.times.10.sup.18 cm.sup.-3 to
1.times.10.sup.20 cm.sup.-3 both inclusive, preferably within a
range of 1.times.10.sup.19 cm.sup.-3 to 1.times.10.sup.20 cm.sup.-3
both inclusive.
[0090] When the thickness of the well layer constituting the third
compound semiconductor layer is determined within a range of 1 nm
to 10 nm both inclusive, and the doping concentration of the
impurity in the barrier layer constituting the third compound
semiconductor layer is determined within a range of
2.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.20 cm.sup.-3 both
inclusive, i.e., when the thickness of the well layer is reduced,
and carriers of the third compound semiconductor layer are
increased, the effect of piezopolarization is allowed to be
reduced, and a laser light source capable of generating an unimodel
optical pulse of short duration having a smaller number of
sub-pulse components is allowed to be obtained. Moreover,
mode-locking drive is allowed to be achieved with a lowest possible
reverse bias voltage, and an optical pulse train in synchronization
with external signals (an electrical signal and an optical signal)
is allowed to be generated. The impurity included in the barrier
layer may be, but not limited to, silicon (Si), and the impurity
may be oxygen (O).
[0091] Alternatively, in the multielectrode type laser diode
element including the above preferred configurations and modes, it
is desirable that the width of the separation groove separating the
second electrode into the first section and the second section be 2
.mu.m or more and 40% or less of a resonator length in the
multielectrode type laser diode element (hereinafter simply
referred to as "resonator length"), preferably 10 .mu.m or more and
20% or less of the resonator length. The resonator length may be
0.6 mm as an example, but is not limited thereto.
[0092] The laser diode element in the laser diode element
assemblies and the methods of driving the same according to the
first to third embodiments of the application including the
above-described various preferred configurations and modes
(hereinafter may be collectively simply referred to as "laser diode
element in the application") may be a laser diode element having a
ridge stripe type separate confinement heterostructure (SCH
structure). Alternatively, the laser diode element may be a laser
diode element having an oblique ridge stripe type separate
confinement heterostructure. In the multielectrode type laser diode
element, a forward bias state is created by passing a DC current
from the first section of the second electrode to the first
electrode through the light emission region, and a voltage (a
reverse bias voltage) is applied between the first electrode and
the second section of the second electrode to apply an electric
field to the saturable absorption region, thereby allowing a
self-pulsation operation and a mode-locking operation to be
performed.
[0093] In the laser diode element in the application, the second
electrode may be configured of a palladium (Pd) single layer, a
nickel (Ni) single layer, a platinum (Pt) single layer, a palladium
layer/platinum layer laminate structure in which the platinum layer
is in contact with a second compound semiconductor layer, or a
palladium layer/nickel layer laminate structure in which the
palladium layer is in contact with the second compound
semiconductor layer. It is to be noted that, in the case where a
lower metal layer is made of palladium, and an upper metal layer is
made of nickel, it is desirable that the thickness of the upper
metal layer be 0.1 .mu.m or more, preferably 0.2 .mu.m or more.
Alternatively, the second electrode is preferably configured of a
palladium (Pd) single layer, and in this case, it is desirable that
the thickness thereof be 20 nm or more, preferably 50 nm or more.
Alternatively, the second electrode is preferably configured of a
palladium (Pd) single layer, a nickel (Ni) single layer, a platinum
(Pt) single layer, or a laminate structure including a lower metal
layer, which is in contact with the second compound semiconductor
layer, and an upper metal layer (where the lower metal layer is
made of one kind of metal selected from the group consisting of
palladium, nickel, and platinum, and the upper metal layer is made
of a metal with an etching rate, in the case where the separation
groove is formed in the second electrode in a step (D) which will
be described later, being equal to, substantially equal to, or
higher than the etching rate of the lower metal layer). Moreover,
it is desirable that an etchant used to form the separation groove
in the second electrode in the step (D) which will be described
later be aqua regia, nitric acid, sulfuric acid, hydrochloric acid,
or a mixed solution of two or more kinds selected from them
(specifically, a mixed solution of nitric acid and sulfuric acid or
a mixed solution of sulfuric acid and hydrochloric acid).
[0094] In the multielectrode type laser diode element, specific
arrangement states of the first section and the second section of
the second electrode include:
[0095] (1) a state where one first section of the second electrode
and one second section of the second electrode are provided, and
the first section of the second electrode and the second section of
the second electrode are disposed with the separation groove in
between;
[0096] (2) a state where one first section of the second electrode
and two second sections of the second electrode are provided, and
an end of the first section faces one of the second sections with
one separation groove in between, and the other end of the first
section faces the other second section with the other separation
groove in between; and
[0097] (3) a state where two first sections of the second electrode
and one second section of the second electrode are provided, and an
end of the second section faces one of the first sections with one
separation groove in between, and the other end of the second
section faces the other first section with the other separation
groove in between (that is, the second electrode has a
configuration in which the second section is sandwiched between the
first sections).
[0098] More broadly, the arrangement states include:
[0099] (4) a state where N first sections of the second electrode
and (N-1) second sections of the second electrode are provided, and
the first sections of the second electrode are arranged with the
second sections of the second electrode in between; and
[0100] (5) a state where N second sections of the second electrode
and (N-1) first sections of the second electrode are provided, and
the second sections of the second electrode are arranged with the
first sections of the second electrode in between.
[0101] It is to be noted that, in other words, the states (4) and
(5) are:
[0102] (4') a state where N light emission regions (carrier
injection regions, gain regions) and (N-1) saturable absorption
regions (carrier non-injection regions) are provided, and the light
emission regions are arranged with the saturable absorption regions
in between; and
[0103] (5') a state where N saturable absorption regions (carrier
non-injection regions) and (N-1) light emission regions (carrier
injection regions, gain regions) are provided, and the saturable
absorption regions are arranged with the light emission regions in
between, respectively.
[0104] Although a method of manufacturing a multielectrode type
laser diode element varies depending on the configuration and
structure of a multielectrode type laser diode element to be
manufactured, the multielectrode type laser diode element is
allowed to be manufactured by, for example, the following method.
More specifically, the multielectrode type laser diode element is
allowed to be manufactured by a method including the following
steps of:
[0105] (A) forming, on a base, a laminate structure body configured
by laminating, in order, a first compound semiconductor layer of a
first conductivity type made of a GaN-based compound semiconductor,
a third compound semiconductor layer made of a GaN-based compound
semiconductor and including a light emission region and a saturable
absorption region, and a second compound semiconductor layer of a
second conductivity type made of a GaN-based compound
semiconductor, the second conductivity type being different from
the first conductivity type;
[0106] (B) forming a second electrode on the second compound
semiconductor layer;
[0107] (C) forming a ridge stripe structure by etching a part or a
whole of the second compound semiconductor layer with use of the
second electrode as an etching mask; and
[0108] (D) forming a resist layer for forming a separation groove
in the second electrode, and then forming the separation groove in
the second electrode by a wet-etching method with use of the resist
layer as a wet-etching mask, thereby separating the second
electrode into the first section and the second section by the
separation groove.
[0109] Then, when such a manufacturing method is adopted,
specifically, when the ridge stripe structure is formed by etching
a part or a whole of the second compound semiconductor layer with
use of the second electrode as an etching mask, i.e., by a
self-alignment system with use of the patterned second electrode as
an etching mask, misalignment between the second electrode and the
ridge stripe structure does not occur. Moreover, the separation
groove is preferably formed in the second electrode by a
wet-etching method. Thus, when the wet-etching method is adopted,
unlike a dry-etching method, deterioration in optical and
electrical characteristics of the second compound semiconductor
layer is allowed to be suppressed. Therefore, deterioration in
light emission characteristics is allowed to be reliably
prevented.
[0110] It is to be noted that, depending on the configuration and
structure of the multielectrode type laser diode element to be
manufactured, in the step (C), the second compound semiconductor
layer may be partially etched in a thickness direction, or the
second compound semiconductor layer may be entirely etched in the
thickness direction, or the second compound semiconductor layer and
the third compound semiconductor layer may be etched in the
thickness direction, or the second compound semiconductor layer and
the third compound semiconductor layer, and further the first
compound semiconductor layer may be partially etched in the
thickness direction.
[0111] Moreover, in the step (D), it is desirable to satisfy
ER.sub.0/ER.sub.1.gtoreq.1.times.10, preferably
ER.sub.0/ER.sub.1.gtoreq.1.times.10.sup.2, where the etching rate
of the second electrode and the etching rate of the laminate
structure body in the case where the separation groove is formed in
the second electrode are ER.sub.0 and ER.sub.1, respectively. When
ER.sub.0/ER.sub.1 satisfies such a relationship, the second
electrode is allowed to be reliably etched without etching the
laminate structure body (or with only slightly etching the laminate
structure body).
[0112] Moreover, in the laser diode element in the application,
specifically, the laminate structure body may be made of an
AlGaInN-based compound semiconductor. Specific AlGaInN-based
compound semiconductors include GaN, AlGaN, GaInN, and AlGaInN.
Moreover, these compound semiconductors may include a boron (B)
atom, a thallium (Tl) atom, an arsenic (As) atom, a phosphorus (P)
atom, or an antimony (Sb) atom at request. Further, it is desirable
that the third compound semiconductor layer (active layer) have a
quantum well structure. More specifically, the third compound
semiconductor layer may have a single quantum well structure (QW
structure) or a multiple quantum well structure (MQW structure).
The third compound semiconductor layer (active layer) with a
quantum well structure has a structure configured by laminating one
or more well layers and one or more barrier layers; however,
examples of a combination of (a compound semiconductor forming the
well layer, a compound semiconductor forming the barrier layer)
include (In.sub.yGa.sub.(1-y)N, GaN), (In.sub.yGa.sub.(1-y)N),
In.sub.zGa.sub.(1-z)N) (where y>z), and (In.sub.yGa.sub.(1-y)N,
AlGaN).
[0113] Moreover, in the laser diode element in the application, the
second compound semiconductor layer may have a superlattice
structure in which p-type GaN layers and p-type AlGaN layers are
alternately laminated, and the thickness of the superlattice
structure may be 0.7 .mu.m or less. When such a superlattice
structure is adopted, while a high refractive index necessary as a
cladding layer is maintained, a series resistance component of the
laser diode element is allowed to be reduced, thereby leading to a
reduction in an operation voltage of the laser diode element. It is
to be noted that the lower limit of the thickness of the
superlattice structure may be, but not limited to, for example, 0.3
.mu.m, and the thickness of the p-type GaN layer constituting the
superlattice structure may be within a range of 1 nm to 5 nm, and
the thickness of the p-type AlGaN layer constituting the
superlattice structure may be within a range of 1 nm to 5 nm, and
the total layer number of the p-type GaN layers and the p-type
AlGaN layers may be within a range of 60 layers to 300 layers.
Further, a distance from the third compound semiconductor layer to
the second electrode may be 1 .mu.m or less, preferably 0.6 .mu.m
or less. When the distance from the third compound semiconductor
layer to the second electrode is determined in such a manner, the
thickness of a p-type second compound semiconductor layer with high
resistance is allowed to be reduced to achieve a reduction in the
operation voltage of the laser diode element. It is to be noted
that the lower limit of the distance from the third compound
semiconductor layer to the second electrode may be, but not limited
to, for example, 0.3 .mu.m. Moreover, the second compound
semiconductor layer is doped with 1.times.10.sup.19 cm.sup.-3 or
more of Mg; and the absorption coefficient of the second compound
semiconductor layer with respect to light with a wavelength of 405
nm from the third compound semiconductor layer is 50 cm.sup.-1 or
more. The atomic concentration of Mg is set on the basis of
material physical properties in which the maximum hole
concentration is exhibited at an atomic concentration of
2.times.10.sup.19 cm.sup.-3, and the atomic concentration of Mg is
a result of design to achieve a maximum hole concentration, i.e.,
minimum resistivity of the second compound semiconductor layer. The
absorption coefficient of the second compound semiconductor layer
is determined to minimize the resistance of the laser diode
element, and as a result, the absorption coefficient of light from
the third compound semiconductor layer is typically 50 cm.sup.-1.
However, the doping amount of Mg may be intentionally set to a
concentration of 2.times.10.sup.19 cm.sup.-3 or more to increase
the absorption coefficient. In this case, the upper limit of the
doping amount of Mg to achieve a practical hole concentration is,
for example, 8.times.10.sup.19 cm.sup.-3. Further, the second
compound semiconductor layer includes an undoped compound
semiconductor layer and a p-type compound semiconductor layer in
order of increasing distance from the third compound semiconductor
layer, and a distance from the third compound semiconductor layer
to the p-type compound semiconductor layer may be
1.2.times.10.sup.-7 m or less. When the distance from the third
compound semiconductor layer to the p-type compound semiconductor
layer is determined in such a manner, internal loss is allowed to
be suppressed without decreasing internal quantum efficiency,
thereby allowing threshold current density at which laser
oscillation starts to be reduced. It is to be noted that the lower
limit of the distance from the third compound semiconductor layer
to the p-type compound semiconductor layer may be, but not limited
to, for example, 5.times.10.sup.-8 m. Moreover, a laminated
insulating film configured of a SiO.sub.2/Si laminate structure is
formed on both side surfaces of the ridge stripe structure; and a
difference in effective refractive index between the ridge stripe
structure and the laminated insulating film may be within a range
of 5.times.10.sup.-3 to 1.times.10.sup.-2. When such a laminated
insulating film is used, a single fundamental transverse mode is
allowed to be maintained even in a high-power operation with over
100 milliwatts. Moreover, the second compound semiconductor layer
may have, for example, a structure configured by laminating an
undoped GaInN layer (p-side light guide layer), an undoped AlGaN
layer (p-side cladding layer), a Mg-doped AlGaN layer (electron
barrier layer), a GaN layer (Mg-doped)/AlGaN layer superlattice
structure (superlattice cladding layer), and a Mg-doped GaN layer
(p-side contact layer) in order of increasing distance from the
third compound semiconductor layer. It is desirable that the band
gap of a compound semiconductor forming the well layer in the third
compound semiconductor layer be 2.4 eV or more. Further, it is
desirable that the wavelength of laser light emitted from the third
compound semiconductor layer (active layer) be within a range of
360 nm to 500 nm, preferably 400 nm to 410 nm. Obviously, the
above-described various configurations may be suitably
combined.
[0114] In the laser diode element in the application, various
GaN-based compound semiconductor layers constituting the laser
diode element are formed on a substrate in order, and in addition
to a sapphire substrate, examples of the substrate include a GaAs
substrate, a GaN substrate, a SiC substrate, an alumina substrate,
a ZnS substrate, a ZnO substrate, an MN substrate, a LiMgO
substrate, a LiGaO.sub.2 substrate, a MgAl.sub.2O.sub.4 substrate,
an InP substrate, a Si substrate, and one of these substrates with
a surface (a main surface) where a base layer or a buffer layer is
formed. In the case where the GaN-based compound semiconductor
layer is formed on the substrate, the GaN substrate is typically
preferable because of low defect density; however, it is known that
the GaN substrate exhibits polarity, nonpolarity, or semipolarity
depending on a growth plane. Further, methods of forming various
GaN-based compound semiconductor layers constituting the laser
diode element include metal organic chemical vapor deposition
methods (a MOCVD method, a MOVPE method), a molecular beam epitaxy
method (a MBE method), a hydride vapor deposition method in which
halogens contribute to transport or reaction, and the like.
[0115] Examples of an organic gallium source gas in the MOCVD
method include a trimethylgallium (TMG) gas and a triethylgallium
(TEG) gas, and examples of a nitrogen source gas include an ammonia
gas and a hydrazine gas. To form a GaN-based compound semiconductor
layer of an n-type conductivity type, for example, silicon (Si) may
be added as an n-type impurity (n-type dopant), and to form a
GaN-based compound semiconductor layer of a p-type conductivity
type, for example, magnesium (Mg) may be added as a p-type impurity
(p-type dopant). When aluminum (Al) or indium (In) is included as a
constituent atom of the GaN-based compound semiconductor layer, a
trimethylaluminum (TMA) gas may be used as an Al source, and
trimethylindium (TMI) gas may be used as an In source. In addition,
a monosilane (SiH.sub.4) gas may be used as a Si source, and a
cyclopentadienylmagnesium gas, methylcyclopentadienylmagnesium, or
bis(cyclopentadienyl)magnesium (Cp.sub.2Mg) may be used as an Mg
source. It is to be noted that, in addition to Si, examples of the
n-type impurity (n-type dopant) include Ge, Se, Sn, C, Te, S, O,
Pd, and Po, and in addition to Mg, examples of the p-type impurity
(p-type dopant) include Zn, Cd, Be, Ca, Ba, C, Hg, and Sr.
[0116] When the first conductivity type is of a n-type conductivity
type, the first electrode electrically connected to the first
compound semiconductor layer of the n-type conductivity type
desirably has a single-layer structure or a multilayer structure
including one or more kinds of metal selected from the group
consisting of gold (Au), silver (Ag), palladium (Pd), aluminum
(Al), titanium (Ti), tungsten (W), copper (Cu), zinc (Zn), tin
(Sn), and indium (In), and examples of such a multilayer structure
may include Ti/Au, Ti/Al, and Ti/Pt/Au. The first electrode is
electrically connected to the first compound semiconductor layer,
and states where the first electrode is electrically connected to
the first compound semiconductor layer include a state where the
first electrode is formed on the first compound semiconductor
layer, and a state where the first electrode is connected to the
first compound semiconductor layer through a conductive material
layer or a conductive substrate. The first electrode and the second
electrode are allowed to be formed by a PVD method such as a vacuum
deposition method or a sputtering method.
[0117] A pad electrode may be formed on the first electrode or the
second electrode to allow the first electrode or the second
electrode to be electrically connected to an external electrode or
circuit. It is desirable that the pad electrode have a single-layer
structure or a multilayer structure including one or more kinds of
metal selected from the group consisting of Ti (titanium), Al
(aluminum), Pt (platinum), Au (gold), and Ni (nickel).
Alternatively, the pad electrode may have a multilayer structure
such as Ti/Pt/Au or Ti/Au.
[0118] In multielectrode type laser diode element, as described
above, for pulsed oscillation, a configuration in which a reverse
bias voltage is applied between the first electrode and the second
section of the second electrode (that is, a configuration in which
the first electrode and the second section are a cathode and an
anode, respectively) is desirable. It is to be noted that a pulse
current applied to the first section of the second electrode, a
pulse current in synchronization with a pulse voltage, or a pulse
voltage may be applied to the second section of the second
electrode, or a DC bias may be applied to the second section of the
second electrode. Moreover, while a current is passed from the
second electrode to the first electrode through the light emission
region, an external electrical signal may be applied from the
second electrode to the first electrode through the light emission
region to be superimposed on the current. Accordingly, laser light
and an external electrical signal are allowed to be synchronized.
Alternatively, an optical signal is allowed to enter from one end
surface of the laminate structure body. Thus, laser light and the
optical signal are allowed to be synchronized. Moreover, in the
second compound semiconductor layer, an undoped compound
semiconductor layer (for example, an undoped GaInN layer or an
undoped AlGaN layer) may be formed between the third compound
semiconductor layer and an electronic barrier layer. Moreover, an
undoped GaInN layer as an optical guide layer may be formed between
the third compound semiconductor layer and the undoped compound
semiconductor layer. The uppermost layer of the second compound
semiconductor layer may be occupied by an Mg-doped GaN layer
(p-side contact layer).
[0119] The laser diode element in the application is applicable to,
for example, fields such as optical disk systems, the
communications field, the optical information field,
opto-electronic integrated circuits, fields of application of
nonlinear optical phenomena, optical switches, various analysis
fields such as the laser measurement field, the ultrafast
spectroscopy field, the multiphase excitation spectroscopy field,
the mass analysis field, the microspectroscopy field using
multiphoton absorption, quantum control of chemical reaction, the
nano three-dimensional processing field, various processing fields
using multiphoton absorption, the medical fields, and the
bio-imaging field.
Example 1
[0120] Example 1 relates to the laser diode element assemblies
according to the first and third embodiments of the application.
FIGS. 1A and 1B illustrate conceptual diagrams of a laser diode
element assembly of Example 1, and FIGS. 1C, 2A and 2B illustrate
schematic plan views of a laser diode element in Example 1.
Moreover, FIG. 3 illustrates a schematic end view of the laser
diode element in Example 1 taken along a direction where a
resonator extends (a schematic end view taken along an XZ plane),
and FIG. 4 illustrates a schematic sectional view taken along a
direction perpendicular to the direction where the resonator
extends (a schematic sectional view taken along a YZ plane). It is
to be noted that FIG. 3 is a schematic end view taken along an
arrow I-I of FIG. 4, and FIG. 4 is a schematic sectional view taken
along an arrow II-II of FIG. 3.
[0121] The laser diode element assembly in Example 1 or Example 2
which will be described later (hereinafter may be collectively
referred to as "laser diode element assembly of Example 1 or the
like") includes a laser diode element 10 and a light reflector 70,
and the laser diode element 10 includes:
[0122] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer 30 of a first
conductivity type (specifically, an n-type conductivity type in
each example) made of a GaN-based compound semiconductor, a third
compound semiconductor layer (active layer) 40 made of a GaN-based
compound semiconductor and including a light emission region (gain
region) 41, and a second compound semiconductor layer 50 of a
second conductivity type (specifically, a p-type conductivity type
in each example) made of a GaN-based compound semiconductor, the
second conductivity type being different from the first
conductivity type;
[0123] (b) a second electrode 62 formed on the second compound
semiconductor layer 50; and
[0124] (c) a first electrode 61 electrically connected to the first
compound semiconductor layer 30.
[0125] Alternatively, the laser diode element assembly of Example 1
or the like includes the laser diode element 10 and an external
resonator 70, and the laser diode element 10 includes:
[0126] (a) a laminate structure body configured by laminating, in
order, the first compound semiconductor layer 30 of a first
conductivity type made of a GaN-based compound semiconductor, the
third compound semiconductor layer 40 made of a GaN-based compound
semiconductor and including the light emission region (gain region)
41, and the second compound semiconductor layer 50 of a second
conductivity type made of a GaN-based compound semiconductor, the
second conductivity type being different from the first
conductivity type;
[0127] (b) the second electrode 62 formed on the second compound
semiconductor layer 50; and
[0128] (c) the first electrode 61 electrically connected to the
first compound semiconductor layer 30.
[0129] Specifically, the laser diode element 10 of Example 1 or the
like is configured of a multielectrode type laser diode element
(more specifically, a bisection type laser diode element), and the
third compound semiconductor layer (active layer) 40 further
includes a saturable absorption region 42, and the second electrode
62 is configured of a first section 62A and a second section 62B,
the first section 62A configured to create a forward bias state by
passing a current to the first electrode 61 through the light
emission region 41, the second section 62B configured to apply an
electric field to the saturable absorption region 42, and the first
section 62A and the second section 62B of the second electrode 62
are separated by a separation groove 62C.
[0130] The laminate structure body includes a ridge stripe
structure 56. Specifically, the laser diode element 10 of Example 1
or the like is a laser diode element having a ridge stripe type
separate confinement heterostructure (SCH structure). More
specifically, the laser diode element is a GaN-based laser diode
element made of index guide type AlGaInN developed for Blu-ray
optical disk systems. Specifically, the first compound
semiconductor layer 30, the third compound semiconductor layer 40,
and the second compound semiconductor layer 50 are made of an
AlGaInN-based compound semiconductor, and more specifically, in the
laser diode element 10 of Example 1 or the like, they have layer
structures illustrated in the following Table 1. In this case,
compound semiconductor layers in Table 1 are listed in order of
decreasing distance from an n-type GaN substrate 21. In addition,
the band gap of a compound semiconductor forming a well layer in
the third compound semiconductor layer 40 is 3.06 eV. The laser
diode element 10 of Example 1 or the like is disposed on a (0001)
plane of the n-type GaN substrate 21, and the third compound
semiconductor layer 40 has a quantum well structure. The (0001)
plane of the n-type GaN substrate 21 is also called "C plane", and
is a crystal plane having polarity.
TABLE-US-00001 TABLE 1 Second compound semiconductor layer 50
p-type GaN contact layer (Mg-doped) 55 p-type GaN (Mg-doped)/AlGaN
superlattice cladding layer 54 p-type AlGaN electron barrier layer
(Mg-doped) 53 Undoped AlGaN cladding layer 52 Undoped GaInN light
guide layer 51 Third compound semiconductor layer 40 GaInN quantum
well active layer (Well layer: Ga.sub.0.92In.sub.0.08N/barrier
layer: Ga.sub.0.98In.sub.0.02N) First compound semiconductor layer
30 n-type GaN cladding layer 32 n-type AlGaN cladding layer 31
Herein, Well layer (two layers) 10.5 nm undoped Barrier layer
(three layers) 14 nm undoped
[0131] Moreover, a part of the p-type GaN contact layer 55 and a
part of the p-type GaN/AlGaN superlattice cladding layer 54 are
removed by an RIE method to form the ridge stripe structure 56. A
laminated insulating film 57 made of SiO.sub.2/Si is formed on both
sides of the ridge stripe structure 56. It is to be noted that the
SiO.sub.2 layer is a lower layer, and the Si layer is an upper
layer. In this case, a difference in effective refractive index
between the ridge stripe structure 56 and the laminated insulating
film 57 is within a range from 5.times.10.sup.-3 to
1.times.10.sup.-2 both inclusive, more specifically
7.times.10.sup.-3. The second electrode (p-side ohmic electrode) 62
is formed on the p-type GaN contact layer 55 corresponding to a top
surface of the ridge stripe structure 56. On the other hand, the
first electrode (n-side ohmic electrode) 61 made of Ti/Pt/Au is
formed on a back surface of the n-type GaN substrate 21.
[0132] In the laser diode element of Example 1 or the like, the
p-type AlGaN electronic barrier layer 53, the p-type GaN/AlGaN
superlattice cladding layer 54, and the p-type GaN contact layer
55, which are Mg-doped compound semiconductor layers, overlap a
light density distribution generated from the third compound
semiconductor layer 40 and its surroundings as little as possible,
thereby reducing internal loss without reducing internal quantum
efficiency. As a result, threshold current density at which laser
oscillation starts is reduced. More specifically, a distance d from
the third compound semiconductor layer 40 to the p-type AlGaN
electronic barrier layer 53 is 0.10 .mu.m, the height of the ridge
stripe structure 56 is 0.30 .mu.m, the thickness of the second
compound semiconductor layer 50 disposed between the second
electrode 62 and the third compound semiconductor layer 40 is 0.50
.mu.m, and the thickness of a portion disposed below the second
electrode 62 of the p-type GaN/AlGaN superlattice cladding layer 54
is 0.40 .mu.m.
[0133] In the laser diode element 10 of Example 1 or the like, the
second electrode 62 is separated by the separation groove 62C into
the first section 62A and the second section 62B, the first section
62A configured to create a forward bias state by passing a DC
current to the first electrode 61 through the light emission region
(gain region) 41, the second section 62B configured to apply an
electric field to the saturable absorption region 42 (the second
section 62B configured to apply a reverse bias voltage to the
saturable absorption region 42 in pulsed oscillation). Herein,
electrical resistance (may be referred to as a "separation
resistance") between the first section 62A and the second section
62B of the second electrode 62 is 1.times.10 times or more,
specifically 1.5.times.10.sup.3 times as high as electrical
resistance between the second electrode 62 and the first electrode
61. The electrical resistance (separation resistance) between the
first section 62A and the second section 62B of the second
electrode 62 is 1.times.10.sup.2.OMEGA. or more, specifically
1.5.times.10.sup.4.OMEGA..
[0134] The laser diode element assembly of Example 1 illustrated in
the conceptual diagram in FIG. 1A has a condensing type external
resonator structure. Moreover, a modification of the laser diode
element assembly of Example 1 illustrated in the conceptual diagram
in FIG. 1B has a collimating type external resonator structure.
Then, the external resonator structure is configured of an end
surface (the other end surface 57B) where a high-reflective coating
layer (HR) is formed closer to the saturable absorption region 42
of the laser diode element and the light reflector (external
resonator) 70, and an optical pulse is extracted from the light
reflector (external resonator) 70. An antireflective coating layer
(AR) is formed on one end surface (the light emission end surface)
57A closer to the light emission region (gain region) 41 of the
laser diode element. As an optical filter, mainly a bandpass filter
(for example, with a central wavelength of 410 nm, a light
transmittance of 90% or more, and a band of 0.8 nm) is used, and
the optical filter is inserted to control the oscillation
wavelength of a laser. As will be described later, mode-locking is
determined by a DC current applied to the light emission region and
the reverse bias voltage applied to the saturable absorption
region. The recurrence frequency f of an optical pulse train is
determined by an external resonator length X', and is represented
by the following formula. Herein, c is the speed of light, and n is
a refractive index of a waveguide.
f=c/(2nX')
[0135] Thus, in the laser diode element assembly of Example 1,
laser light is emitted from the one end surface 57A of the ridge
stripe structure 56, and a part of the laser light is reflected by
the light reflector 70 to be returned to the laser diode element
10, and a remaining part of the laser light exits to outside
through the light reflector 70. Moreover, laser light is reflected
by the other end surface 57B of the ridge stripe structure 56.
Alternatively, laser light is emitted from the one end surface 57A
of the ridge stripe structure 56, and the laser light is reflected
by the external resonator 70 to be returned to the laser diode
element 10, and laser light emitted from the one end surface 57A or
the other end surface 57B (specifically, from the one end surface
57A in Example 1) of the ridge stripe structure 56 exits to
outside. Then, the minimum width W.sub.min and a maximum width
W.sub.max of the ridge stripe structure 56 satisfy
1<W.sub.max/W.sub.min<3.3(=10/3) or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3(=40/3), and laser light
exiting to outside is single-mode light.
[0136] More specifically, in the laser diode element in Example 1,
laser light is emitted from the one end surface (light emission end
surface) 57A closer to the light emission region of the laminate
structure body. For example, an antireflective coating layer (AR)
or a low-reflective coating layer with a reflectivity of 0.5% or
less, preferably 0.3% or less is formed on the one end surface (the
light emission end surface) 57A. Moreover, a high-reflective
coating layer (HR) with a reflectivity of 85% or more, preferably
95% or more is formed on the other end surface (light reflection
end surface) 57B facing the one end surface (light emission end
surface) 57A in the laser diode element 10. It is to be noted that
the antireflective coating layer (AR), the low-reflective coating
layer, and the high-reflective coating layer (HR) are not
illustrated. The saturable absorption region 42 is disposed in a
portion of the laminate structure body, the portion located closer
to an end surface (the other end surface 57B in Example 1) opposite
to an end surface (the one end surface 57A in Example 1) where
laser light exits to outside. As the antireflective coating layer
or the low-reflective coating layer, a laminate structure including
two or more kinds of layers selected from the group consisting of a
titanium oxide layer, a tantalum oxide layer, a zirconia oxide
layer, a silicon oxide layer, and an aluminum oxide layer may be
used.
[0137] In Example 1, the light reflector 70 or the external
resonator 70 is configured of a half mirror.
[0138] As described above, it is desirable that the second
electrode 62 having separation resistance of
1.times.10.sup.2.OMEGA. or more be formed on the second compound
semiconductor layer 50. In the case of the GaN-based laser diode
element, unlike a GaAs-based laser diode element in related art,
mobility in a p-type conductivity type compound semiconductor is
small; therefore, without increasing resistance by performing ion
implantation or the like on the second compound semiconductor layer
50 of the p-type conductivity type, the second electrode 62 formed
on the second compound semiconductor layer 50 of the p-type
conductivity type is separated by the separation groove 62C,
thereby allowing electrical resistance between the first section
62A and the second section 62B of the second electrode 62 to be 10
or more times as high as electrical resistance between the second
electrode 62 and the first electrode 61, or allowing the electrical
resistance between the first section 62A and the second section 62B
of the second electrode 62 to be 1.times.10.sup.2.OMEGA. or
more.
[0139] In the laser diode element 10 illustrated in the schematic
plan view in FIG. 1C, the width on the one end surface (light
emission end surface) 57A of the ridge stripe structure 56 is the
maximum width W.sub.max, and the width on the other end surface
(light reflection end surface) 57B of the ridge stripe structure 56
is the minimum width W.sub.min. The width of the ridge stripe
structure 56 having a so-called flare structure is gradually and
linearly reduced from the one end surface 57A to the other end
surface 57B. It is to be noted that, in FIGS. 1C, 2A, 2B, 14, 18A,
and 18B, a separation groove region is diagonally shaded to specify
the separation groove 62C.
[0140] In the laser diode element 10 illustrated in a schematic
plan view in FIG. 2A, the width of a portion, corresponding to the
first section 62A of the second electrode 62, of the ridge stripe
structure 56 is the maximum width W.sub.max at the one end surface
(light emission end surface) 57A and the minimum width W.sub.min at
a side facing the separation groove 62C, that is, the width of the
portion of the ridge stripe structure 56 is gradually and linearly
reduced from the maximum width W.sub.max to the minimum width
W.sub.min. The width of a portion, corresponding to the second
section 62B of the second electrode 62, of the ridge stripe
structure 56 is fixed at the minimum width W.sub.min.
[0141] In the laser diode element 10 illustrated in a schematic
plan view in FIG. 2B, the width of a portion, corresponding to the
first section 62A of the second electrode 62, of the ridge stripe
structure 56 is the maximum width W.sub.max in a certain region
from the one end surface (light emission end surface) 57A, and the
minimum width W.sub.min at a side facing the separation groove 62C,
that is, the width of the portion of the ridge stripe structure 56
is gradually and linearly reduced to the minimum width W.sub.min
from the certain region (with the maximum width W.sub.max). The
width of a portion, corresponding to the second section 62B, of the
second electrode 62 of the ridge stripe structure 56 is fixed at
the minimum width W.sub.min.
[0142] However, the planar shapes of the first section 62A and the
second section 62B of the second electrode 62 are not limited to
the examples illustrated in FIGS. 1C, 2A, and 2B.
[0143] The ridge stripe structure 56 has a so-called flare
structure, and the minimum width W.sub.min of the ridge stripe
structure 56 satisfies 1.times.10.sup.-6
m.ltoreq.W.sub.min.ltoreq.3.times.10.sup.-6 m.
[0144] As the laser diode element illustrated in FIG. 2A, laser
diode elements in which the resonator length of the laser diode
element 10 was 600 .mu.m, and lengths of the first section 62A, the
second section 62B, and the separation groove 62C of the second
electrode 62 were 560 .mu.m, 30 .mu.m, and 10 .mu.m, respectively,
W.sub.min was 1.5 .mu.m, and W.sub.max was changed to values
indicated in the following Table 2 were prototyped.
TABLE-US-00002 TABLE 2 W.sub.max (.mu.m) W.sub.max/W.sub.min
Example 1A 2.5 1.7 Reference Example 1B 5.0 3.3 Example 1C 10.0 6.7
Example 1D 15.0 10.0 Example 1E 20.0 13.3
[0145] Likewise, as the laser diode element illustrated in FIG. 2A,
a laser diode element (Example 1F) in which the resonator length of
the laser diode element 10 was 600 .mu.m, the lengths of the first
section 62A, the second section 62B, and the separation groove 62C
of the second electrode 62 were 560 .mu.m, 30 .mu.m, and 10 .mu.m,
W.sub.min was 2.5 .mu.m, and W.sub.max was 15.0 .mu.m
(W.sub.min/W.sub.max=6.0) was prototyped.
[0146] While a current I.sub.g is passed to the first electrode 61
through the first section 62A of the second electrode 62 and the
light emission region 41, a current is passed to the second section
62B of the second electrode 62 through the first electrode 61 and
the saturable absorption region 42 (specifically, a reverse bias
voltage is applied between the second section 62B of the second
electrode 62 and the first electrode 61), thereby allowing
single-mode pulsed oscillation to be performed. Moreover, while the
current I.sub.g is passed to the first electrode 61 through the
first section 62A of the second electrode 62 and the light emission
region 41, a current is passed to the first electrode 61 through
the second section 62B of the second electrode 62 and the light
emission region 41 (specifically, a forward bias voltage is applied
between the second section 26B of the second electrode 62 and the
first electrode 61), or a current is not passed to the first
electrode 61 through the second section 62B of the second electrode
62 and the light emission region 41, thereby allowing single-mode
continuous-wave oscillation to be performed. It is to be noted that
applying a reverse bias voltage means that the second section 62B
of the second electrode 62 and the first electrode 61 are an anode
and a cathode, respectively, and a potential difference is V.sub.sa
(V.sub.sa<0 with reference to the potential of the second
section 62B of the second electrode 62), and applying a forward
bias voltage means that the second section 62B of the second
electrode 62 and the first electrode 61 are a cathode and an anode,
respectively, and the potential difference is V.sub.sa
(V.sub.sa>0 with reference to the potential of the first
electrode 61).
[0147] As illustrated in Table 3, oscillation states and
oscillation modes of respective samples when the current I.sub.g
was passed to the samples, and the voltage V.sub.sa was applied to
the samples were evaluated. While the results are illustrated in
Table 3, near-field images in Example 1A in the case of (W.sub.min,
W.sub.max)=(1.5 .mu.m, 2.5 .mu.m) are illustrated in FIGS. 6A and
6B, near-field images in Reference Example 1B and Comparative
Example 1B in the case of (W.sub.min, W.sub.max)=(1.5 .mu.m, 5.0
.mu.m) are illustrated in FIGS. 7A to 7C, near-field images in
Example 1C and Comparative Example 1C in the case of (W.sub.min,
W.sub.max)=(1.5 .mu.m, 10.0 .mu.m) are illustrated in FIGS. 8A to
8C, near-field images in Example 1D and Comparative Example 1D in
the case of (W.sub.min, W.sub.max)=(1.5 .mu.m, 15.0 .mu.m) are
illustrated in FIGS. 9A to 9C, near-field images in Example 1E and
Comparative Example 1E in the case of (W.sub.min, W.sub.max)=(1.5
.mu.m, 20.0 .mu.m) are illustrated in FIGS. 10A to 10C, and
near-field images in Example 1F and Comparative Example 1F in the
case of (W.sub.min, W.sub.max)=(2.5 .mu.m, 15.0 .mu.m) are
illustrated in FIGS. 11A to 11C. It is to be noted that Comparative
Example 1B, Comparative Example 1C, Comparative Example 1D,
Comparative Example 1E, and Comparative Example 1F correspond to
laser diode element assemblies of Reference Example 1B, Example 1C,
Example 1D, Example 1E, and Example 1F, respectively, from which
the light reflector 70 or the external resonator 70 is removed.
TABLE-US-00003 TABLE 3 I.sub.g V.sub.sa Oscillation Reference
X.sub.max (mA) (V) State Mode Drawing X.sub.min = 1.5 .mu.m 2.5
.mu.m Example 1A 145 -15 Pulsed Single FIG. 6A 45 +4 Continuous-
Single FIG. 6B wave 5.0 .mu.m Reference 170 -7 Pulsed Multi FIG. 7A
Example 1B 100 +4 Continuous- Multi FIG. 7B wave Comparative 100 +4
Continuous- Multi FIG. 7C Example 1B wave 10.0 .mu.m Example 1C 360
-7 Pulsed Single FIG. 8A 180 +4 Continuous- Multi FIG. 8B wave
Comparative 180 +4 Continuous- Multi FIG. 8C Example 1C wave 15.0
.mu.m Example 1D 265 -9 Pulsed Single FIG. 9A 185 +4 Continuous-
Single FIG. 9B wave Comparative 185 +4 Continuous- Multi FIG. 9C
Example 1D wave 20.0 .mu.m Example 1E 285 -9 Pulsed Single FIG. 10A
200 +4 Continuous- Single FIG. 10B wave Comparative 200 +4
Continuous- Multi FIG. 10C Example 1E wave X.sub.min = 2.5 .mu.m
15.0 .mu.m Example 1F 290 -9 Pulsed Single FIG. 11A 190 +4
Continuous- Single FIG. 11B wave Comparative 190 +4 Continuous-
Multi FIG. 11C Example 1F wave
[0148] Herein, in the case of 1<W.sub.max/W.sub.min<3.3, that
is, in Example 1A with W.sub.max/W.sub.min=5/3, single-mode pulsed
oscillation and single-mode continuous-wave oscillation were
obtained.
[0149] Moreover, in the case of 3.3W.sub.max/W.sub.min<6, that
is, in Reference Example 1B and Comparative Example 1B with
W.sub.max/W.sub.min=10/3, in pulsed oscillation or continuous-wave
oscillation, single-mode oscillation was not obtained, but
multi-mode oscillation was obtained.
[0150] Further, in the case of
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3, that is, in Example 1C
with W.sub.max/W.sub.min=20/3, in pulsed oscillation, single-mode
oscillation was obtained, but in continuous-wave oscillation,
multi-mode oscillation was obtained, and in Example 1D with
W.sub.max/W.sub.min30/3, and Example 1E with
W.sub.max/W.sub.min=40/3, in pulsed oscillation, single-mode
oscillation was obtained, and in continuous-wave oscillation,
single-mode oscillation was also obtained. On the other hand, in
Comparative Examples 1C, 1D, and 1E, single-mode oscillation was
not obtained, but multi-mode oscillation was obtained.
[0151] Moreover, in Example 1F with W.sub.max/W.sub.min=15.0
.mu.m/2.5 .mu.m=6.0, in pulsed oscillation, single-mode oscillation
was obtained, and in continuous-wave oscillation, single-mode
oscillation was also obtained. On the other hand, in Comparative
Example 1F, single-mode oscillation was not obtained, but
multi-mode oscillation was obtained.
[0152] Further, a laser diode element assembly with
W.sub.min=W.sub.max was formed as Comparative Example 1. When, a
relative value E.sub.out/E.sub.0 of light intensity E.sub.out of
laser light emitted from the laser diode element assembly was
determined where light intensity of laser light exiting to outside
in the laser diode element assembly of Comparative Example 1 is
E.sub.0, the following results were obtained. It is to be noted
that FIG. 12 illustrates a relationship between the width of the
ridge stripe structure 56 and pulse energy of laser light emitted
from the laser diode element assembly in pulsed oscillation, and
the larger the value of W.sub.max is, the more the area of a gain
section increased, thereby increasing the pulse energy of laser
light.
TABLE-US-00004 E.sub.out/E.sub.0 E.sub.out/E.sub.0 (pulsed
oscillation) (continuous-wave oscillation) Example 1A 1.6 1.5
Example 1C 2.3 Example 1D 2.6 5.5 Example 1E 3.2 7.2 Example 1F 4.3
5.8
[0153] Thus, in the laser diode element assembly of Example 1 or
the method of driving the same, an external resonator structure and
the ridge stripe structure 56 having a so-called flare structure
with a specified relationship between the minimum width W.sub.min
and the maximum width W.sub.max are included; therefore, higher
power is allowed to be achieved, and single-mode laser light is
allowed to be emitted.
[0154] Characteristics which may be necessary for the second
electrode 62 are as follows.
[0155] (1) The second electrode 62 functions as an etching mask
when the second compound semiconductor layer 50 is etched.
[0156] (2) The second electrode 62 is allowed to be wet-etched
without deteriorating optical and electrical characteristics of the
second compound semiconductor layer 50.
[0157] (3) The second electrode 62 has contact resistivity of
10.sup.-2 .OMEGA.cm.sup.2 or less when the second electrode 62 is
formed on the second compound semiconductor layer 50.
[0158] (4) When the second electrode 62 has a laminate structure, a
material forming a lower metal layer has a large work function, and
low contact resistivity with respect to the second compound
semiconductor layer 50, and is allowed to be wet-etched.
[0159] (5) When the second electrode 62 has a laminate structure, a
material forming an upper metal layer has resistance to etching
(for example, a Cl.sub.2 gas used in a RIE method) performed when a
ridge stripe structure is formed, and is allowed to be
wet-etched.
[0160] In the laser diode element in Example 1 or the like, the
second electrode 62 is configured of a Pd single layer with a
thickness of 0.1 .mu.m.
[0161] It is to be noted that the p-type GaN/AlGaN superlattice
cladding layer 54 having a superlattice structure in which p-type
GaN layers and p-type AlGaN layers are alternately laminated has a
thickness of 0.7 .mu.m or less, more specifically 0.4 .mu.m, and
the p-type GaN layer constituting the superlattice structure has a
thickness of 2.5 nm, and the p-type AlGaN layer constituting the
superlattice structure has a thickness of 2.5 nm, and the total
layer number of the p-type GaN layers and the p-type AlGaN layers
is 160. Moreover, a distance from the third compound semiconductor
layer 40 to the second electrode 62 is 1 .mu.m or less, more
specifically 0.5 .mu.m. Further, the p-type AlGaN electronic
barrier layer 53, the p-type GaN/AlGaN superlattice cladding layer
54, and the p-type GaN contact layer 55 constituting the second
compound semiconductor layer 50 are doped with 1.times.10.sup.19
cm.sup.-3 or more (more specifically, 2.times.10.sup.19 cm.sup.-3)
of Mg, and the absorption coefficient of the second compound
semiconductor layer 50 with respect to light with a wavelength of
405 nm is 50 cm.sup.-1 or more, more specifically 65 cm.sup.-1.
Moreover, the second compound semiconductor layer 50 includes, in
order of increasing distance from the third compound semiconductor
layer 40, undoped compound semiconductor layers (the undoped GaInN
light guide layer 51 and the undoped AlGaN cladding layer 52) and
p-type compound semiconductor layers, and a distance (d) from the
third compound semiconductor layer 40 to the p-type compound
semiconductor layers (specifically, the p-type AlGaN electron
barrier layer 53) is 1.2.times.10.sup.-7 m or less, specifically
100 nm.
[0162] A method of manufacturing the laser diode element in Example
1 will be described below referring to FIGS. 15A, 15B, 16A, 16B,
and 17. It is to be noted that FIGS. 15A, 15B, 16A, and 16B are
schematic partial sectional views of a substrate and the like taken
along a YZ plane, and FIG. 17 is a schematic partial end view of
the substrate and the like taken along an XZ plane.
[0163] [Step-100]
[0164] First, a laminate structure body configured by laminating,
in order, the first compound semiconductor layer 30 of the first
conductivity type (the n-type conductivity type) made of a
GaN-based compound semiconductor, the third compound semiconductor
layer (active layer) 40 made of a GaN-based compound semiconductor
and including the light emission region (gain region) 41 and the
saturable absorption region 42, and the second compound
semiconductor layer 50 of the second conductivity type (the p-type
conductivity type) made of a GaN-based compound semiconductor, the
second conductivity type being different from the first
conductivity type is formed on a base, more specifically, on a
(0001) plane of the n-type GaN substrate 21 by a known MOCVD method
(refer to FIG. 15A).
[0165] [Step-110]
[0166] After that, the second electrode 62 is formed on the second
compound semiconductor layer 50. More specifically, a Pd layer 63
is entirely formed by a vacuum deposition method (refer to FIG.
15B), and then a resist layer for etching is formed on the Pd layer
63 by a photolithography technique. Then, a part not covered with
the resist layer for etching of the Pd layer 63 is removed with use
of aqua regia, and then the resist layer for etching is removed.
Thus, a structure illustrated in FIG. 16A is allowed to be
obtained. It is to be noted that the second electrode 62 may be
formed on the second compound semiconductor layer 50 by a liftoff
method.
[0167] [Step-120]
[0168] Next, the ridge stripe structure 56 is formed by etching a
part or a whole of the second compound semiconductor layer 50 with
use of the second electrode 62 as an etching mask. More
specifically, a part of the second compound semiconductor layer 50
is etched by a RIE method using a Cl.sub.2 gas with use of the
second electrode 62 as an etching mask. Thus, a structure
illustrated in FIG. 16B is allowed to be obtained. As the ridge
stripe structure 56 is formed through a self-alignment system with
use of, as an etching mask, the patterned second electrode 62,
misalignment does not occur between the second electrode 62 and the
ridge stripe structure 56.
[0169] [Step-130]
[0170] After that, a resist layer 64 for forming the separation
groove in the second electrode 62 is formed (refer to FIG. 17). It
is to be noted that a reference numeral 65 indicates an opening
disposed in the resist layer 64 to form the separation groove.
Next, the separation groove 62C is formed in the second electrode
62 by a wet-etching method with use of the resist layer 64 as a
wet-etching mask to separate the second electrode 62 by the
separation groove 62C into the first section 62A and the second
section 62B. More specifically, the separation groove 62C is formed
in the second electrode 62 by immersing the entire structure in
aqua regia used as an etchant for approximately 10 seconds. Then,
the resist layer 64 is removed. Thus, a structure illustrated in
FIGS. 3 and 4 is allowed to be obtained. When the wet-etching
method, but not a dry-etching method, is adopted in such a manner,
optical and electrical characteristics of the second compound
semiconductor layer 50 are not deteriorated. Therefore, light
emission characteristics of the laser diode element are not
deteriorated. It is to be noted that, in the case where the
dry-etching method is adopted, internal loss .alpha..sub.i of the
second compound semiconductor layer 50 may be increased to cause an
increase in threshold voltage or a decline in light output. In this
case, ER.sub.0/ER.sub.1.apprxeq.1.times.10.sup.2 is established,
where the etching rate of the second electrode 62 is ER.sub.0, and
the etching rate of the laminate structure body is ER.sub.1. Since
there is a high etching selection ratio between the second
electrode 62 and the second compound semiconductor layer 50, the
second electrode 62 is allowed to be etched reliably without
etching the laminate structure body (or with only slightly etching
the laminate structure body). It is to be noted that it is
desirable to satisfy ER.sub.0/ER.sub.1.ltoreq.1.times.10,
preferably ER.sub.0/ER.sub.1.ltoreq.1.times.10.sup.2.
[0171] The second electrode 62 may have a laminate structure
including a lower metal layer made of palladium (Pd) with a
thickness of 20 nm and an upper metal layer made of nickel (Ni)
with a thickness of 200 nm. In wet-etching with use of aqua regia,
the etching rate of nickel is approximately 1.25 times as high as
that of palladium.
[0172] [Step-140]
[0173] After that, the formation of an n-side electrode, cleavage
of a substrate, and the like are performed, and packaging is
further performed, thereby allowing the laser diode element 10 to
be formed.
[0174] Typically, resistance R (.OMEGA.) of a semiconductor layer
is represented by the following formula with use of resistivity p
(.OMEGA.m) of a material forming the semiconductor layer, the
length X.sub.0 (m) of the semiconductor layer, the sectional area S
(m.sup.2) of the semiconductor layer, carrier density n
(cm.sup.-3), electrical charge e (C), and mobility
.mu.(m.sup.2/Vs).
R = ( .rho. X 0 ) / S = X 0 / ( n e .mu. S ) ##EQU00001##
[0175] Since the mobility of a p-type GaN-based semiconductor is
two or more orders of magnitude smaller than that of a p-type
GaAs-based semiconductor, electrical resistance is easily
increased. Therefore, it is clear from the above formula that a
laser diode element including a ridge stripe structure with a small
sectional area has large electrical resistance.
[0176] As a result of measuring electrical resistance between the
first section 62A and the second section 62B of the second
electrode 62 of the formed laser diode element 10 by a
four-terminal method, the electrical resistance between the first
section 62A and the second section 62B of the second electrode 62
was 15 k.OMEGA. in the case where the width of the separation
groove 62C was 20 .mu.m. Moreover, when, in the formed laser diode
element 10, a DC current was passed from the first section 62A of
the second electrode 62 to the first electrode 61 through the light
emission region 41 to create a forward bias state, and an electric
field was applied to the saturable absorption region 42 by applying
a reverse bias voltage between the first electrode 61 and the
second section 62B of the second electrode 62, a self-pulsation
operation was allowed to be performed. In other words, the
electrical resistance between the first section 62A and the second
section 62B of the second electrode 62 was 10 or more times as high
as the electrical resistance between the second electrode 62 and
the first electrode 61, or 1.times.10.sup.2.OMEGA. or more.
Therefore, a leakage current flowing from the first section 62A of
the second electrode 62 to the second section 62B is allowed to be
reliably suppressed, and as a result, the light emission region 41
is allowed to be brought into a forward bias state, and the
saturable absorption region 42 is allowed to be reliably brought
into a reverse bias state, thereby allowing a single-mode
self-pulsation operation to be reliably achieved.
Example 2
[0177] Example 2 relates to the laser diode element assemblies
according to the second and third embodiments of the application.
Conceptual diagrams of the laser diode element assembly of Example
2 are illustrated in FIGS. 5A and 5B. It is to be noted that an
example illustrated in FIG. 5A is of a condensing type, and an
example illustrated in FIG. 5B is of a collimating type.
[0178] In the laser diode element assembly of Example 2, laser
light is emitted from one end surface 58A of the ridge stripe
structure 56, and the laser light is reflected by a light reflector
71 to be returned to the laser diode element 10, and a part of the
laser light exits to outside from the other end surface 58B of the
ridge stripe structure 56. Moreover, in Example 2, the light
reflector 71 or an external resonator 71 is configured of a total
reflection mirror. Then, an external resonator structure is
configured of the other end surface 58B of a laser diode element in
which a reflective coating layer (R) is formed closer to the
saturable absorption region 42 (the other end surface 58B) and the
light reflector (external resonator) 71, and an optical pulse is
extracted from the saturable absorption region 42. An
antireflective coating layer or a low-reflective coating layer (AR)
is formed on the one end surface 58A closer to the light emission
region (gain region) 41 of the laser diode element.
[0179] The configuration and structure of the laser diode element
assembly of Example 2 are similar to those of the laser diode
element assembly of Example 1 except for the above-described
points, and will not be further described in detail. It is to be
noted that, even in Example 2, the minimum width W.sub.min, and the
maximum width W.sub.max of the ridge stripe structure 56 satisfy
1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min13.3, and laser light exiting to
outside is single-mode light.
[0180] It is to be noted that the width on the one end surface 58A
of the ridge stripe structure 56 is the maximum width W.sub.max,
and the width on the other end surface 58B of the ridge stripe
structure 56 is the minimum width W.sub.min. The ridge stripe
structure 56 has a so-called flare structure, and the minimum width
W.sub.min of the ridge stripe structure 56 satisfies
1.times.10.sup.-6 m.gtoreq.W.sub.min.ltoreq.3.times.10.sup.-6 m.
Moreover, as in the case of Example 1, the laser diode element 10
is configured of a multielectrode type laser diode element (more
specifically, a bisection type laser diode element), and the
saturable absorption region 42 is disposed in a portion of the
laminate structure body, the portion located closer to the other
end surface 58B opposite to the one end surface 58A. In Example 2,
as results of various tests, in a relationship between
W.sub.max/W.sub.min, pulsed oscillation/continuous-wave
oscillation, and single-mode/multi-mode, results similar to those
in Example 1 were obtained.
[0181] Although the present application is described referring to
preferred examples, the application is not limited thereto.
Configurations and structures of the laser diode element and the
laser diode element assembly described in the preferred examples
are examples, and may be modified as appropriate. Moreover, in the
examples, various values are indicated, but the values are also
examples; therefore, for example, when the specifications of the
laser diode element to be used are changed, the values are also
changed.
[0182] For example, in a modification of the laser diode element 10
illustrated in a schematic plan view in FIG. 18A, the ridge stripe
structure 56 has the maximum width W.sub.max at the one end surface
(light emission end surface) 57A, and the minimum width W.sub.min,
at the other end surface (light reflection end surface) 57B. Then,
an angle where an end section corresponding to the first section
62A of the second electrode 62 of the ridge stripe structure 56
forms with an axis line of the ridge stripe structure 56 is larger
than an angle where an end section corresponding to the second
section 62B of the second electrode 62 of the ridge stripe
structure 56 forms with the axis line of the ridge stripe structure
56. A modification of the laser diode element 10 illustrated in
FIG. 18A is illustrated in a schematic plan view in FIG. 18B, and
in the laser diode element 10, the width of a portion,
corresponding to the first section 62A of the second electrode 62,
of the ridge stripe structure 56 is the maximum width W.sub.max in
a certain region from the one end surface (light emission end
surface) 57A. Then, the width of the ridge stripe structure 56 is
reduced from the certain region to the other end surface (light
reflection end surface) 57B. In this case, the angle where the end
section corresponding to the first section 62A of the second
electrode 62 of the ridge stripe structure 56 forms with the axis
line of the ridge stripe structure 56 is larger than the angle
where the end section corresponding to the second section 62B of
the second electrode 62 of the ridge stripe structure 56 forms with
the axis line of the ridge stripe structure 56.
[0183] Moreover, the second electrode may have a laminate structure
including a lower metal layer made of palladium (Pd) with a
thickness of 20 nm and an upper metal layer made of nickel (Ni)
with a thickness of 200 nm. It is to be noted that, in wet-etching
with use of aqua regia, the etching rate of nickel is approximately
1.25 times as high as that of palladium.
[0184] The number of the light emission regions 41 or the saturable
absorption regions 42 is not limited to one. FIG. 13 illustrates a
schematic end view (a schematic end view taken along an XZ plane)
of a laser diode element including one first section 62A of the
second electrode and two second sections 62B.sub.1 and 62B.sub.2 of
the second electrode. In the laser diode element, one end of the
first section 62A faces one second section 62B.sub.1 with one
separation groove 62C.sub.1 in between, and the other end of the
first section 62A faces the other second section 62B.sub.2 with the
other separation groove 62C.sub.2 in between. Thus, one light
emission region 41 is sandwiched between two saturable absorption
regions 42.sub.1 and 42.sub.2.
[0185] The laser diode element may be a laser diode element having
an oblique ridge stripe type separate confinement heterostructure
with an oblique waveguide. An example in which the laser diode
element described in Example 1 or Example 2 includes the oblique
ridge stripe structure having an oblique waveguide is illustrated
in FIG. 14, which is a schematic top view of a ridge stripe
structure 56'. The laser diode element includes a structure formed
by combining two linear ridge stripe structures, and it is
desirable that an angle .theta. where the two ridge stripe
structures intersect with each other be, for example,
0<.theta..ltoreq.10 (degrees), preferably 0<.theta..ltoreq.6
(degrees). When the oblique ridge stripe structure is adopted, the
reflectivity of an end surface coated with an antireflective
coating AR is allowed to approach an ideal value of 0%, and as a
result, advantages that the generation of laser light going round
in the laser diode element is allowed to be prevented, and the
generation of subsidiary laser light associated with main laser
light is allowed to be suppressed are allowed to be obtained.
[0186] In the examples, the laser diode element is disposed on a C
plane, i.e., a {0001} plane which is a polar plane of the n-type
GaN substrate 21. In such a case, it may be difficult to
electrically control saturable absorption by the QCSE effect
(quantum confined Stark effect) by an internal electrical field
caused by piezopolarization and spontaneous polarization in the
third compound semiconductor layer. In other words, in some cases,
to obtain a self-pulsation operation and a mode-locking operation,
it may be necessary to increase the value of a DC current passed to
the first electrode or the value of a reverse bias voltage applied
to the saturable absorption region, or a sub-pulse component
associated with a main pulse is generated, or it is difficult to
synthesize an external signal and an optical pulse. To suppress
such phenomena, the laser diode element may be disposed on a
nonpolar plane such as an A plane, i.e., a {11-20} plane, an M
plane, i.e., a {1-100} plane, or a {1-102} plane, or a semipolar
plane such as a {11-2n} plane including a {11-24} plane or a
{11-22} plane, a {10-11} plane, or a {10-12} plane. Thus, even if
piezopolarization and spontaneous polarization are generated in
third compound semiconductor layer of the laser diode element,
piezopolarization is not generated in the thickness direction of
the third compound semiconductor layer, and piezopolariztaion is
generated in a direction substantially perpendicular to the
thickness direction of the third compound semiconductor layer;
therefore, an adverse effect caused by piezopolarization and
spontaneous polarization is allowed to be eliminated. It is to be
noted that the {11-2n} plane means a nonpolar plane forming an
angle of substantially 40.degree. with respect to the C plane.
Moreover, in the case where the laser diode element is disposed on
the nonpolar plane or the semipolar plane, the limit (within a
range of 1 nm to 10 nm both inclusive) of the thickness of the well
layer and the limit (within a range of 2.times.10.sup.18 cm.sup.-3
to 1.times.10.sup.20 cm.sup.-3 both inclusive) of the doping
concentration of the impurity in the barrier layer are allowed to
be eliminated.
[0187] It is to be noted that the application is allowed to have
the following configurations.
[0188] (1) A laser diode element assembly including:
[0189] a laser diode element; and
[0190] a light reflector,
[0191] in which the laser diode element includes
[0192] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0193] (b) a second electrode formed on the second compound
semiconductor layer, and
[0194] (c) a first electrode electrically connected to the first
compound semiconductor layer,
[0195] the laminate structure body includes a ridge stripe
structure,
[0196] laser light is emitted from a first end surface of the ridge
stripe structure, and a part of the laser light is reflected by the
light reflector to be returned to the laser diode element, and a
remaining part of the laser light exits to outside through the
light reflector,
[0197] the laser light is reflected by a second end surface of the
ridge stripe structure, and
[0198] a minimum width W.sub.min and a maximum width W.sub.max of
the ridge stripe structure satisfy 1<W.sub.max/W.sub.min<3.3
or 6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3.
[0199] (2) A laser diode element assembly including:
[0200] a laser diode element; and
[0201] a light reflector,
[0202] in which the laser diode element includes
[0203] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0204] (b) a second electrode formed on the second compound
semiconductor layer, and
[0205] (c) a first electrode electrically connected to the first
compound semiconductor layer,
[0206] the laminate structure body includes a ridge stripe
structure,
[0207] laser light is emitted from a first end surface of the ridge
stripe structure, and the laser light is reflected by the light
reflector to be returned to the laser diode element,
[0208] a part of the laser light exits to outside from a second end
surface of the ridge stripe structure, and
[0209] a minimum width W.sub.min and a maximum width W.sub.max of
the ridge stripe structure satisfy 1<W.sub.max/W.sub.min<3.3
or 6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3.
[0210] (3) A laser diode element assembly including:
[0211] a laser diode element; and
[0212] an external resonator,
[0213] in which the laser diode element includes
[0214] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0215] (b) a second electrode formed on the second compound
semiconductor layer, and
[0216] (c) a first electrode electrically connected to the first
compound semiconductor layer,
[0217] the laminate structure body includes a ridge stripe
structure,
[0218] laser light is emitted from a first end surface of the ridge
stripe structure, and the laser light is reflected by the external
resonator to be returned to the laser diode element,
[0219] laser light emitted from the first end surface or a second
end surface of the ridge stripe structure exits to outside, and
[0220] a minimum width W.sub.min and a maximum width W.sub.max of
the ridge stripe structure satisfy 1<W.sub.max/W.sub.min<3.3
or 6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3.
[0221] (4) The laser diode element assembly according to any one of
(1) to (3), in which
[0222] the light reflector is configured of a mirror, a chirped
mirror, a volume Bragg grating, or a fiber Bragg grating.
[0223] (5) The laser diode element assembly according to any one of
(1) to (3), in which
[0224] the laser light exiting to outside is single-mode light.
[0225] (6) The laser diode element assembly according to any one of
(1) to (3), in which
[0226] 1.times.10.sup.-6
m.ltoreq.W.sub.min.ltoreq.3.times.10.sup.-6 m is satisfied.
[0227] (7) The laser diode element assembly according to any one of
(1) to (3), in which
[0228] the third compound semiconductor layer further includes a
saturable absorption region,
[0229] the second electrode is configured of a first section and a
second section, the first section configured to create a forward
bias state by passing a current to the first electrode through the
light emission region, the second section configured to apply an
electric field to the saturable absorption region, and
[0230] the first section and the second section of the second
electrode are separated by a separation groove.
[0231] (8) The laser diode element assembly according to (7), in
which
[0232] the saturable absorption region is disposed in a portion of
the laminate structure body, the portion located closer to an end
surface opposite to an end surface where laser light exits to
outside.
[0233] (9) The laser diode element assembly according to (7), in
which
[0234] the laser light exiting to outside is pulsed oscillation
laser light.
[0235] (10) The laser diode element assembly according to (9), in
which the saturable absorption region is disposed in a portion of
the laminate structure body, the portion located closer to an end
surface opposite to an end surface where laser light exits to
outside.
[0236] (11) The laser diode element assembly according to any one
of (1) to (3), in which
[0237] the laser light exiting to outside is continuous-wave
oscillation laser light.
[0238] (12) The laser diode element assembly according to any one
of (1) to (3), in which
[0239] light intensity E.sub.out of laser light emitted from the
laser diode element assembly satisfies E.sub.out/E.sub.01.5, where
light intensity of laser light exiting to outside assuming that
W.sub.min=W.sub.max is established is E.sub.0.
[0240] (13) A method of driving a laser diode element assembly, the
laser diode element assembly including a laser diode element and a
light reflector, the laser diode element including
[0241] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0242] (b) a second electrode formed on the second compound
semiconductor layer, and
[0243] (c) a first electrode electrically connected to the first
compound semiconductor layer,
[0244] the third compound semiconductor layer further including a
saturable absorption region,
[0245] the second electrode being configured of a first section and
a second section, the first section configured to create a forward
bias state by passing a current to the first electrode through the
light emission region, the second section configured to apply an
electric field to the saturable absorption region,
[0246] the first section and the second section of the second
electrode being separated by a separation groove,
[0247] the laminate structure body including a ridge stripe
structure,
[0248] laser light being emitted from a first end surface of the
ridge stripe structure, and a part of the laser light being
reflected by the light reflector to be returned to the laser diode
element, and a remaining part of the laser light exiting to outside
through the light reflector,
[0249] the laser light being reflected by a second end surface of
the ridge stripe structure,
[0250] a minimum width W.sub.min and a maximum width W.sub.max of
the ridge stripe structure satisfying
1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3,
[0251] the method including:
[0252] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the second section of the second
electrode through the first electrode and the saturable absorption
region, thereby allowing pulsed oscillation to be performed;
and
[0253] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the first electrode through the second
section of the second electrode and the light emission region, or
not passing a current to the first electrode through the second
section of the second electrode and the light emission region,
thereby allowing continuous-wave oscillation to be performed.
[0254] (14) A method of driving a laser diode element assembly, the
laser diode element assembly including a laser diode element and a
light reflector, the laser diode element including
[0255] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0256] (b) a second electrode formed on the second compound
semiconductor layer, and
[0257] (c) a first electrode electrically connected to the first
compound semiconductor layer,
[0258] the third compound semiconductor layer further including a
saturable absorption region,
[0259] the second electrode being configured of a first section and
a second section, the first section configured to create a forward
bias state by passing a current to the first electrode through the
light emission region, the second section configured to apply an
electric field to the saturable absorption region,
[0260] the first section and the second section of the second
electrode being separated by a separation groove,
[0261] the laminate structure body including a ridge stripe
structure,
[0262] laser light being emitted from a first end surface of the
ridge stripe structure, and the laser light being reflected by the
light reflector to be returned to the laser diode element,
[0263] a part of the laser light exiting to outside from a second
end surface of the ridge stripe structure,
[0264] a minimum width and a maximum width W.sub.max of the ridge
stripe structure satisfying 1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3,
[0265] the method including:
[0266] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the second section of the second
electrode through the first electrode and the saturable absorption
region, thereby allowing pulsed oscillation to be performed;
and
[0267] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the first electrode through the second
section of the second electrode and the light emission region, or
not passing a current to the first electrode through the second
section of the second electrode and the light emission region,
thereby allowing continuous-wave oscillation to be performed.
[0268] (15) A method of driving a laser diode element assembly, the
laser diode element assembly including a laser diode element and an
external resonator, the laser diode element including
[0269] (a) a laminate structure body configured by laminating, in
order, a first compound semiconductor layer of a first conductivity
type made of a GaN-based compound semiconductor, a third compound
semiconductor layer made of a GaN-based compound semiconductor and
including a light emission region, and a second compound
semiconductor layer of a second conductivity type made of a
GaN-based compound semiconductor, the second conductivity type
being different from the first conductivity type,
[0270] (b) a second electrode formed on the second compound
semiconductor layer, and
[0271] (c) a first electrode electrically connected to the first
compound semiconductor layer,
[0272] the third compound semiconductor layer further including a
saturable absorption region,
[0273] the second electrode being configured of a first section and
a second section, the first section configured to create a forward
bias state by passing a current to the first electrode through the
light emission region, the second section configured to apply an
electric field to the saturable absorption region,
[0274] the first section and the second section of the second
electrode being separated by a separation groove,
[0275] the laminate structure body including a ridge stripe
structure,
[0276] laser light being emitted from a first end surface of the
ridge stripe structure, and the laser light being reflected by the
external resonator to be returned to the laser diode element,
[0277] laser light emitted from the first end surface or a second
end surface of the ridge stripe structure exiting to outside,
[0278] a minimum width W.sub.min, and a maximum width W.sub.max of
the ridge stripe structure satisfying
1<W.sub.max/W.sub.min<3.3 or
6.ltoreq.W.sub.max/W.sub.min.ltoreq.13.3,
[0279] the method including:
[0280] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the second section of the second
electrode through the first electrode and the saturable absorption
region, thereby allowing pulsed oscillation to be performed;
and
[0281] while passing a current to the first electrode through the
first section of the second electrode and the light emission
region, passing a current to the first electrode through the second
section of the second electrode and the light emission region, or
not passing a current to the first electrode through the second
section of the second electrode and the light emission region,
thereby allowing continuous-wave oscillation to be performed.
[0282] (16) The method of driving a laser diode element assembly
according to any one of (13) to (15), in which
[0283] the saturable absorption region is disposed in a portion of
the laminate structure body, the portion located closer to an end
surface opposite to an end surface where laser light exits to
outside.
[0284] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the present subject matter and without diminishing its
intended advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *